Your mom works in a lab making Pokémon more human-like. They do this for many reasons, some more obvious than others, on an island far off the main land of any region, since this kind of experimentation, isn't exactly legal.

You live on the same site as the enormous laboratory. Your mom has already experimented on some of your Pokémon (your choice), and they all live with you. They have gained human speech and a more human body shape.