It's hard to set financial boundaries when your significant other has kids. When this woman feels conflicted about her husband's kids, she asks Reddit:
My (28f) husband (35m) and I have been married for a year, we dated for two years prior to that. When we met I said I didn't want to have kids of my own, but wouldn't mind being in a relationship with someone who has kids.
We came to the agreement that he would be solely responsible for his kids, minus the little stuff. I love my husband a lot and his kids are alright, the older two are great but the younger two are a bit much.
We have had separate finances our whole relationship, since he has kids and I don't. When I moved into his house we agreed that I would pay 1/4 of the mortgage, since it's a 4 bed and 3/4 rooms go to his kids.