Prepositions, Smepositions

BB is learning more and more words each day. He is trying to put words that he knows together into sentences. Sometimes he does well - "I like car," "that my mommy," other times, not so well. He knows the words on, off, up, down, but he doesn't quite understand what the words mean just yet. He'll ask "light on?" when he wants to turn the light off. He also alternates the use of up and down when he's done eating at the table, so I'm never quite sure if he wants down on the ground, or up in my lap. This wouldn't be a big deal if he wasn't practically 2 with no hindsight, foresight, or self-control. I'm a ESOL teacher to an egomaniac student.