Kids should always be put first, if for no other reason than they are kids. Yes they do grow up, and yes adults do deserve happiness (going back a bit in this tread) but not at the expense of childeren. I do resent my father for putting his needs/desires ahead of mine when I was growing up. But I'm 100% fine with my mother's remarriage of a few years ago and her focusing her attention on her husband, but I'm an adult now, different rules apply.

Not to sound sexist but men tend to be a bit more self centered when it comes to relationships, but that doesn't make it right. Trust your instincts it seems a bit of a red flag that you seem more concerned for how his kids will take your introduction to them than he is.