What is the 80s movie where an Alien kid speaks only in commercials to a brother and sister on a spaceship?

There is an 80's movie where a brother and sister (I think) end up on a spaceship (I forget how?) with an Alien kid. The alien only knows how to speak English from hearing TV and radio signals from earth so he talks in an announcer's voice. This was a family type of movie and the alien "kid" was sort of chubby, green and had they goofy antenae. I cannot find it anywhere, does anyone remember this?