AITA for telling my kids why I don’t buy their half sibling anything?

Family finances and blended relationships can be incredibly sensitive topics, especially when infidelity is involved. In this case, a father of two (10‑year‑old son and 9‑year‑old daughter) recounts how he explained to his children why he refuses to buy gifts or cover expenses for their half-sibling—the result of his ex-wife’s affair during their marriage.

Despite having always been transparent about the half-sibling not being his biological child, the conversation took an unexpected turn when the ex-wife, struggling financially, pressured him to help out. When he firmly reiterated his stance to his kids, she lashed out, accusing him of cruelty. Now, he wonders if his honest explanation makes him the asshole or if he was right to set such clear boundaries.

‘AITA for telling my kids why I don’t buy their half sibling anything?’

The mother of my two children (10m and 9f) cheated on me during our marriage and became pregnant with another man’s child. I learned this when I caught her with the man in question and after quizzing her, she admitted there was a strong chance he was the father of the baby she was pregnant with.

I ended our marriage right there and took a DNA test when her youngest was born and she was not mine. So in the divorce custody and support was only factored in for our two kids. I paid some child support because I made more than her but we had 50-50 custody time with the kids and I remained an involved dad.

My ex lived with her youngest’s father October of last year when he took off without a word and dipped from their lives. She has been in pursuit of child support ever since but he cannot be found and he quit the last known job he had, so she has been unsuccessful so far. This has led to her struggling and I buy more for the kids we share so they don’t suffer because of the failed relationship with the affair partner.

Last month my ex told me she was struggling to keep up with the expenses for her youngest and she asked me if I would maybe buy some stuff that included her too. I said no, that I was responsible for my kids and I would not become financially responsible in any way for the child she made while cheating on me.

She begged and told me they will have different lives if I don’t help at least for now and I told her that was not my problem and maybe she’ll think about that in the future before she starts an ongoing affair. She told our kids about asking me and encouraged them to ask me for them.

The kids were confused because they have always known their half sister is not my child but they started to doubt because of how their mom talked (saying good men take care of all their children and loving a child who is part of your family should never be that hard).

The kids approached me and asked me about it and told me their mom wanted them to ask me for stuff for their half sister. So I explained to them that she is not my child or part of my family but she is still part of theirs. They asked why since my oldest has some memories of his mom and I being together while she was pregnant.

I said their mom got pregnant with their half sister while we were together but DNA proved she was not mine and I did not raise her for that reason. I told them I am still their dad and nothing has changed but I was never really their half sister’s dad and don’t want to buy her stuff like I do for them.

They understood and when they went back to their mom’s she called and cussed me out for telling the kids more details than she wanted them to know. I said they had always been aware they had a different dad to her other child and that needed to remain clear because I was not claiming her now that her father has abandoned her. She called me a cruel d**k.. AITA?

Family and relationship experts emphasize that setting clear financial and emotional boundaries is crucial in blended family situations—especially when the origins of the relationship involve infidelity. Experts like Dr. Laura Markham note, “Honesty about your values and boundaries is essential in guiding children to understand their family structure,” which applies here as the father sought to protect his own children’s best interests.

When a parent’s past decisions have directly affected the family dynamic, it’s both reasonable and necessary to delineate responsibilities clearly. In this case, the father is asserting that his obligation is only to his biological children, not to cover the financial needs of a child conceived through an affair.

While the ex-wife’s argument for unity and shared responsibility may come from a place of wanting a stable family environment for all the children, experts agree that boundaries should be maintained to avoid blurring roles and responsibilities. This approach helps ensure that the children receive consistent expectations and protects the parent’s financial autonomy—an important consideration when past behavior has already disrupted the family’s equilibrium.

Here’s the input from the Reddit crowd:

Community reactions on platforms like Reddit are mixed but often sympathetic toward parents who must make tough choices in complex situations. Many commenters agree that if you’re clear about your responsibilities and have been upfront about the family’s structure from the beginning, you’re within your rights to maintain that boundary.

Others, however, suggest that a more gentle explanation might have mitigated the hurt feelings involved. Still, the prevailing view is that a parent’s primary duty is to protect and provide for their own children, and that financial responsibility should not be extended simply because of shared living arrangements or familial obligations, especially when the situation originates from past infidelity.

zombiezmaj −  NTA. I’d be tempted to offer to take primary custody of your 2 kids to relieve her of their financial burden so she can just worry about her youngest.

MrsPomMummy −  NTA. Your ex tried to make you out to be the bad guy and force your hand, banking on you not wanting to involve the kids. That was super wrong of her and good on you for not taking it. Stand your ground there. That being said, when she says she can’t afford stuff for the youngest kid, are we talking fun things like toys or basic necessities like diapers?

Obviously you are neither responsible for the youngest kid nor are you the a**hole for refusing to engage. Your ex made her mess. But if it’s the latter and you can afford it, I would consider buying her occassional basic necessities if you get the feeling that she genuinely cannot afford them (not just giving her money).

Ultimately, the kid would be the one suffering and she is innocent in all of that. I would use it to show to your kids the importance of being compassionate, even to strangers you have no responsibility towards (and stress that!!!).

author124 −  NTA – you’re not obligated to financially support your kids’ half-sister, and it doesn’t sound like your explanation encouraged a divide between them or similar; if your ex didn’t want them to have more information about the situation at hand, she shouldn’t have tried to use them to manipulate you.

tinyd71 −  This is a terrible situation for kids. They shouldn’t be involved in any issues between their parents. So you’re stuck either looking like the bad guy for not telling them why you are treating their sibling differently, or you have to buy in to the dynamic of telling your children information that isn’t any of their business at ages 9 and 10. NTA for not wanting to support a child that isn’t yours. And NTA for telling your kids (the hopefully age-appropriate) truth.

Pink_Cloud90 −  NTA. Obviously you don’t have to buy things for a kid that isn’t yours and isn’t part of your life. she called and cussed me out for telling the kids more details than she wanted them to know. She told our kids about asking me and encouraged them to ask me for them.

This is terrible. That she actually used the kids to get the money. When you told her you’re not going to do this. If she didn’t want them to know more, she shouldn’t have encouraged them to go to you and ask about it. Thats a really s**tty move to put the kids in between all of this.

ReviewOk929 −  NTA. 1. She is the AH for involving the children in this. 2. She is the AH for having an affair. 3. The other dude is the AH for running out on HIS child. 4. She is the AH for not wanting her kids to know the whole truth and manipulating children. 5. You are defo not the AH

Beck2010 −  NTA. I’m not a lawyer, but have read some articles where a non biological parent can be made financially responsible if they have a record of supporting the child. For that reason alone, I wouldn’t increase support. Your ex is awful for involving your kids in her troubles. She created this issue, she needs to deal with it.

Abstruse −  NTA. She’s the one who sent the kids to ask you. What precisely did she think was going to happen? She had to know there was a strong chance of you still saying “no”, meaning the kids — being kids — would immediately ask “Why?” Everybody wants to find someone else to blame when they get to the FO stage of FAFO.

silverwheelspinner −  I can see some posters advocating for compassion but where would it end? Once the ex wife sees the OP providing, she won’t stop asking. It’ll be prom dress, car , college fund etc. It’s not the kid’s fault but completely understand why OP doesn’t want to support the child.

sephyir −  Well, NTA. I’m strongly against talking badly about the other parent to shared kids (no matter how justified), but here it was your ex who muddled the waters and clarification was needed. I do feel sorry for the youngest kid though, not her fault that your ex cheated or her father left, but she’s going to pay for it. Still, clearly not your responsibility.

Ultimately, this story isn’t about being unloving—it’s about setting and maintaining clear boundaries in a complicated family dynamic. The father’s decision to only support his own children financially is rooted in the reality of their family history and his commitment to his biological kids. While the bluntness of his explanation may have hurt his ex-wife’s feelings, it also reinforced an important lesson for his children about honesty and responsibility.

What do you think? Is it reasonable for a parent to limit their financial support to their own biological children in a blended family? Or should there be more flexibility to accommodate all members of the household? Share your thoughts and experiences in the comments below.