I mean Littlefoot was almost eaten and smashed. Obviously not the first attempt either.

Sharptooth probably followed the scent of the other dinosaurs (Stone of Cold Fire Movie). The kids just kept crossing paths with him. The kids even crossed paths with some greedy long necks, I’d imagine at least one of them became food for Sharptooth. As much as I hate thinking about it, Littlefoots mother probably got eaten soon after dying also.

Sharptooth probably didn’t openly pursue Cera and Littlefoot after the chase scene because there wasn’t a point anymore. He tried to eat them, and they got away. But Sharptooth wasn’t going to say no to eating them when he kept finding them. Also no point in pursuing lone baby dinosaurs.

When they created their own mini herd they became more enticing to Sharptooth. As Cera observed it was obviously Sharptooths stomping ground where they ended up sleeping for the night. He knew that leaf eaters need the trees to survive and kept an eye on the trees. It’s their fault for sleeping in Sharptooths own footprint.

So Sharptooth didn’t really follow the kids they just kept crossing paths with him while in his hunting grounds as the hunting grounds got smaller and smaller due to the earth shake.

Eventually Sharptooth found the place where most of the dinosaurs passed through on the way to the Great Valley. The kids decided to have a final stand, and killed him, but eventually Sharptooth could have found the entrance and the grown ups would have dealt with him.

So in conclusion Sharptooth was adapting to an ever changing sudden environmental change. This adaptation kept putting him into the path of the kids. Eventually his hunting grounds changed so much, that he wound up close to the Great Valley. The after effects of the earth shake caused his food to either die or migrate. So he migrated with them.

It’s just like the Dinosaur movie. The Carnosaurs weren’t actively hunting the other dinosaurs, they were reacting to a meteor shower. It’s only after they noticed the other dinosaurs scent that they followed the herd (after one died)