Shiloh was a child too, right?

So, I'm thinking about and half-way (make that quarter-way) editing my novel Shiloh's Children. I originally split the novel into three parts:

1. Michigan -- this describes Shiloh's childhood, her getting married, her having kids, and the tragedy that strikes the family (currently 16,000 words)
2. U.S. -- describes where the kids are now that they are grown (currently 12,000 words)
3. World -- the kids go on a trip (currently 22,000 words)

I am having trouble with section one. I could make section one into this huge, gigantic, epic section that goes on and on like old classic books. Or, I could make it super duper short. Or somewhere in the middle. I mean, Shiloh had a childhood too, right? That should be included. But her childhood is not the major action of the book. Yet, it is an important part as to why the major action takes place. I'm leaning toward 20,000 words for this section. It will probably end up being more, though. That is, if I ever stop blogging and start editing! We'll see...