How to discover genealogy of another sim?

[twiggy84]

Hi there. Been playing Sims 3 for a while now on X-Box 360. One thing I still haven't figured out how to do, and maybe one of you knows, how do I tell who a child belongs to that isn't in my family? My sim girl has a boyfriend and one day he brought a kid over with him to their house. How do I tell who the child belings to? I need to know if he's been sleeping around on her, lol.

[TheChronicR]

There's no possible way I can think of, other than taking control of the child through cheats.