An alien who has stolen something valuable from a creepy black and white lady (also an alien) crashes on Earth. He has a pet that looks like a black and white fox-like creature with no mouth. The alien looks like a young boy. A young girl finds him and let's him live with her.
At one point he shrinks a Brontosaurus skeleton at a museum to give to her, but I think she chastises him for doing so. She somehow manages to help him leave Earth to escape black humanoid aliens with pincers for hands who are sent by the creepy alien lady.
I think I read this around 1997-9. It was in English. It was a book, but I can't remember if it was hardback or not. I don't think it was in a series. It was in colour and the style was... unique? I honestly can't remember reading anything else that looked like it.
My mother seems to think it was called something like Jojo/Joejoe from Outer Space. But I don't know if she is right.