They’re 11 and 9. I’m not their biological father. I also didn’t adopt them. I was with their mom and in their lives for 5 years, but I don’t consider them my kids.
Let's be a little more clear. I assume you're a man. I assume the person you have referred to as your "ex" is actually your wife. I assume "they" are her kids. If the kids are 11 and 9, and you've only been in the picture for 5 years, I assume that means you got married to your wife at least 4 years after the younger child was born. Are all of those assumptions correct?
My ex says I acted as their father though by taking them to school and going to their sports games and since I lived with them and took care of them sometimes her friend says that’s enough to get child support from me. Is she right?
Is your wife an attorney? Is her friend an attorney? I'm guessing not. Thus, who cares what these people say?
Taking your wife's kids from a prior relationship to school and going to sports games is not "act[ing] as their father" any more than it is acting as a stepfather or a boyfriend or even a non-romantic partner. And, even if that weren't the case, "act[ing] as their father" doesn't magically make you liable for child support. By the way, where is/are the actual father(s)? Is your wife receiving child support from him/them?
What do you do about what?
If I'm wrong and this woman isn't your wife (either because you're already divorced or because you were never married in the first place), then there isn't anything to do about anything.
On the other hand, if I'm right, then what you do depends on whether there's a divorce action pending or not. If there's a divorce case pending or, if there's no divorce case pending but you want a divorce, then get yourself to a divorce lawyer. If no divorce is yet pending and you don't want to be divorced, then there isn't anything to be done.
