To be honest, LBT 5 was one of my least-watched LBT films (seen it all the way through only twice), but I'll try my best to comment, as I consider LBT 2 one of the strongest overall LBT films, and I have a lot of exposure to it.
I believe that bringing Chomper back, at least in the matter that Universal chose to, was somewhat inappropriate. He was a very interesting addition to LBT 2. The aspect of Chomper's parents decending into the Great Valley to retrieve their child, while the Valley inhabitants were horrified to see what had come to their homeland, added in the aspect of multiculturalism, and I feel it even somewhat reflects back to our own world: No matter what the Human Race does, we will never live in peace with one another. It's not in our biological nature; just like the Sharpteeth depend on the leafeaters for food, humans depend on beliefs. Conflicts in beliefs directly translate into cultural conflicts, which may, in turn lead to physical conflicts (ie. war. See the Middle East, the Holy Land, and the United States, with Religion as the central issue in many cases, as a case study.)
Anyways, Chomper's character in LBT 2 was suitable. The fact that no wounds were shown when Cera was bitten does not surprise me. This is very typical of the series, and wounds are generally only shown either:
1) On a central character in a Very important scene, such as Littlefoot's mother's wound after being bitten, or Doc's scar in LBT 6.
2) On an "evil" character, showing that he has been overcome or weakened. See the sharptooth battle near the end of LBT 5.
The series Never shows a child character being wounded, probably mainly due to the sensitivity of the issue. If Chomper would have bitten Cera hard enough to have drawn blood and caused a more serious injury, perhaps the Gang would have been a little more cautious around Chomper, but there is no edivence that he could bite through the thick hide of a dinosaur. Even when he attacks the Egg eaters, they were stunned for a few seconds, but no damage was done. I honestly don't think he had the jaw strength or control to bite Through a dinosaur hide as a newborn. Perhaps sharpteeth's parents break down the meat before the young feast on it.
I can't help but think that Chomper must feel guilty about eating someone who can talk to him, and he can understand. Time has progressed enough that Chomper must have eaten Something between when he was born, and when the gang found him again (aside from insects, I mean, what Sharptooth lives on insects? Maybe baby sharpteeth, I don't know...

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If a sharptooth becomes tame, it will not survive. A hunter's only chance for survival, unless it's a scavenger, is to attack and eat its' prey. Therefore, Chomper must have eaten some sort of meat during his life. Perhaps his parents killed all of his food before he even saw it, so he was never exposed to killing a leafeater. Possible, yes. However I have trouble believing that Chomper's parents would hide a rudimentary skill like hunting from Chomper's exposure. It is necessary for his survival, so one would think that his parents would be concerned that he be exposed to it, and learn how to hunt for himself, as early in his life as possible.
There is not any Hard evidence that Chomper is "tame", as we never see him exposed to any leafeaters aside from his Friends. I do, however, have a difficult time believing that, especially since Chomper clearly states that there isn't much to eat on the Island, he isn't somehow tempted to devour his friends at some point. Though perhaps he's so excited to meet someone he knows, that it didn't even cross his mind to any extent.
The island Must be larger than it appears, as we never see a single leafeater on the island. There must be Some, or the sharpteeth would never have ended up there in the first place, though now they have no choice but to remain, unless they hitch a ride across Big Water from a sharptooth swimmer or something

I don't know where they could go with that.
I honestly don't know what Chomper would do in the event that he ran into a leafeater that he didn't know, and I think we need to know this before we can decide whether or not Chomper is truly Tame. If he is tame, then I seriously worry about his survival. Otherwise, Chomper is simply a sharptooth with a good heart, and a bilingual tongue

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