It is possible for parents and grandparents to structure their lives around it being convenient for the traditional role. The fact that American society doesn't do this is a bit of a tragedy. I know families that engage the entire extended family, including grandparents, in raising the next generation.

(In fact, its an evolutionary thing. It answers the question of why does evolution keep grandparents around and healthy? Generally, when an organism no longer serves a useful purpose towards propagation of the species, it dies.)