Thank you for all the replies. I read a few gardening blogs and it would seem the only thing I will grow by planting my onion is an onion flower. The seeds from which will potentially grow onions.
I may just set in some water and let it root in the kitchen window and use the greens. My son (almost 3) does not like onions (if only he knew how many he eats w/out knowing) and is convinced that if I plant it in the garden it will ruin his pumpkins, cucumbers and tomatoes. So worried in fact that there were tears.