Lets see... I'll try to come up with some adjectives for certain character's personalities...
Littlefoot: Brave, good leader, intelligent
Cera: Rash, headstrong, proud
Ducky: Kind, small, weak
Petrie: Insecure, fast (at flying)
Ruby: Fast (on her feet, at least), vocal
Spike: Mute, gluttonous, strong
Chomper: Predator, nice, potentially deadly in the future.
Pterano: Bad leader, schemer,
Tops: Strict, strong, proud
Tria: Kind, weak, hedonistic
Bron: Strong, good leader (?)
Ducky's mother: Kind, loving, motherly
Petrie's mother: Kind, loving, motherly
Littlefoot's grandfather: Old, wise, still strong
Littlefoot's grandmother: Old, emotional, weak
Mo: Playful, loud, sometimes annoying
Mr. Thicknose: Wise, old, sometimes liar...
Tricia: Cute, very young...
Guido: Insecure, odd, confused
Redclaw: Strong, fierce, has some leadership capabilities
Ali: Shy, kind, migratory
Littlefoot's mother: Kind, motherly, weak