[Alouette]

In the book, there is a strong development of a father-son relationship

I thought it was more of an older brother/younger brother, but you are right, they did reverse the ages in the film. In the book, Sam is younger than Frodo (who is about 50 in hobbit-years, which would be ~ thirtysomething in human years)

[Tax-chick]

I think you're probably closer on that ... my boys are all still at the "fight like wolf puppies" stage, so I wasn't thinking of brothers :-).