Probable Explanations

[Noname]

There are more than a few. First, there is the issue of how Chomper got off that island, if and his parents did too. Presumably, because Ruby says that she told his parents that she'd take care of him, they got off the island too, or Ruby's family visited the island at one point.

Then, there is the matter of how Red Claw came to be such a menace. No explanations are given. And why Chomper's parents aren't with him.

There are many others, I am sure.

[LBTDiclonius]

Well, for getting off the island, some theory's are that the path appears and dissapears due to the tide. So maybe they got off that way. And Chomper's parents probably aren't with him because of the simple fact, they are sharpteeth. And Sharpteeth aren't allowed into the valley. Chomper was nice enough, not to mention he could actually persuade the residants (with some minor help from his friends) and assure them that he was good. His parents on the other hand probably could never, and I doubt that even with the help of Littlefoot and the gang, nobody would trust two full grown sharpteeth coming into the valley. Maybe if they agreed to stay outside the valley they could stay with Chomper. But maybe they needed to give their son time to get away from Redclaw after escaping from the island and are still trying to hunt him down and fend him off.

These explanations are never given. And sorry for mine being so long. But that's my theory.