When I've dated women in the past who were divorced and had children I never felt threatened. Call it (ego) but I've always felt like I was an "upgrade". LOL!
Seriously I would rather be with someone who has worked out a good working relationship with their ex concerning their children than to be with someone who is constantly complaining about their ex, going to court to fight for child support, or using their children as pawns to hurt one another. Simply put I hate drama.
Having said that I can understand how someone might be jealous of their mate spending a lot of time with their ex as a "family".
Several years ago a friend of mine was dating a woman while he was divorced from his wife who resided in Denmark with their two children. One summer she decided to come visit him with the children for a month long visit. His girlfriend lived in the same apartment complex. Essentially he told her that he would not be able to see her for a month because he did not want to confuse his kids or risk upsetting his ex. According to him he slept on the sofa for the entire month.
During that period he did take the kids along with his ex to amusement parks, beach outings, movies, dinners, and they swam in the apartment complex swimming pool. When his ex and the children flew back to Denmark he spoke with the girl he was dating and she said she was done with him. My friend felt like this girl should have understood he wanted to make sure that his little kids had a quality visit with him and she should have been understanding.
When I asked him if it had been the "other way around" would he have been as understanding and he claims that he would have. If I'm being honest and I were in a situation where my girlfriend put me on ice for a month and her ex was spending all that time overnight with her and their kids.... I would not have put my life on hold either.