@MadDoctor61 I don't think answering no would have split up the children playing at the park, but answering yes might have. They always ask to come over, which I've always assumed meant they would come to my sims' house, even when my sims weren't there. If my assumption is correct, saying yes would mean the child would leave your child and go with his mother to your sms' house. But I don't remember ever testing out that theory. They might just come to wherever your sims are.
So what did you do? And how did it turn out?