Happy Little Submarine: Space Pals.

Under Professor Penguin and Mayor Seal's misguided rules, the undersea society is convinced that "Aliens are harmful". But when Olly stumbles upon a little alien named Wugu, who comes to Earth for a visit and gets lost from his family, it's Olly to the rescue. During their journey, Olly realizes that aliens are not dangerous at all, but in fact, quite friendly. Now Olly and his friends must keep Professor Penguin from executing his evil plans in order to help Wugu find a way home.