If the filler would rather have them as kids, I'd like something very fluffy and silly; basically Yamcha and everyone's respective parents dealing with the kids' puppy crushes on Yamcha (Yamcha doesn't encourage it, of course--he just thinks its kind of adorable). Maybe the kids argue over who Yamcha likes more, one of them blurting out at a function (and embarrassing everyone) that they're going to marry Yamcha when they get older, etc.