For me, "Train," has subtle negative connotations.
It could just be me.
You train dogs.
You train some plants to grow, "Here." and nowhere else.
Train has no notion of thinking for one's self.
Dedicate is more something that's addressing the parent's heart. If the one reading the verse (we're presuming a parent,) is having their own heart and perspective addressed (please do this rather than force that other person to do this,) it's more gentle, and more fair because it's a bit like the kid arguing that Jimmy over there doesn't (fill in the blank,) and the mother says, "I'm talking to you, not Jimmy." It's like the verse that says, "Children obey your parents." It doesn't say, "parents force your children to obey you," but rather says, "Parents do not provoke your children." Everyone gets instruction, but not to force the other party.
Dedicate a child in the way he should go, has a sense of gentle commitment.
Train has visions of whips and chairs.