I say it's a bad idea.
If you really liked her and saw a future with her then the kid might not be a problem, but the fact that you're moving says that this will just end up as something casual, which won't be good for any of you, especially her kid.
End it now, not only so you don't get mixed up in something that's so serious you're not ready for it, but also so you don't end up hurting her kid.