This half twin airplane aficionado that I babysit for named Matt proposed this question to a certain teacher of Sunday School: "Where is God?"
Her Answer, both simple and universal enough for a child to grasp without actually really understanding (because, if you get down to it, the question wasn't actually answered) was that "God is everywhere."
Finding the answer insufficient, and perhaps feeling belittled, Matt asked "How did God create himself?"
The teacher was unable to answer this, instead choosing to laugh-and-ignore. I kept my pride on the DL.