Hmmm. I don't think it's a question of the song not being that brave; the song was trying to correct an underlying assumption of the 1970s, which was that any boy who wanted a doll (and, to a lesser extent, any girl who played with cars and trucks and liked sports-at least past the age when such things were "cute") either was gay or would be turned gay by playing with toys reserved for the opposite gender. There would have been no point in telling the parents of the 1970s that William was gay; most parents of the time probably would have been wondering (even if they didn't say so) if a little boy who wanted a doll had some tendencies "that way." William's father is clearly worried about this, and is trying to steer his son away from dolls toward sports...and a more heteronormative male role. And the song delivers a Take That, for Grandma points out to William's father that the traditional male role could use expanding--and that it would be GOOD for William to be able to care for and demonstrate his love for his child.

The song was saying that a boy not only could but SHOULD like things that were traditionally tagged feminine, that a father's role could be nurturing and could involve feeding and diapering a baby, rather than leaving all of that to the mother, and that things people thought of as "for girls only" should be valued by everyone. Those were pretty revolutionary messages back then.