This isn't meant as a joke. It is meant as a serious question because the thing is seeing as how they came to be biologically they would have no need for them. So if they didn't have bellybuttons their children in turn should not because you can't inherit something your parents don't have. If they did have bellybuttons why would they have been created wth them?
This is just someting to think about i'm not trying to break down the bible or christianity here. This is meant to be one of those kind of questions lik which came first the chicken or the egg? In fact its very much like that.