One of the hard things about this ride is not knowing which variation you'll get, so if the child's first ride is one of the milder songs, things could go really well. But if the first ride is "Born To Be Wild," well... On the bright side, if that one goes well, all the other songs will be a piece of cake.
Oldest had no problem with TOT as soon as he was tall enough and loves GOTG. But he loved challenging himself, even if he didn't really enjoy the ride. He would go on something over and over just to prove that he could, not because he loved it. Youngest didn't enjoy TOT (and wasn't ready at 6) and doesn't like GOTG. Loves Screamin', Soarin', SM, ST, RSR, etc. Just doesn't really care for TOT/GOTG's drops or suspense. I think a lot of it is not knowing which song is coming, and by the time you find out (if it's a variation you don't like), it's too late. As other's have said, each kid is different!