How do explain God to a 2-year-old?

Tough one. But don't simply carried away with silly clarifications to the innocent kid who might develop a predetermined perception. Encourage humanity and thankfulness. Teach him mutual respect. Lt him thank someone for everything that he do - have a meal, got a new toy etc. Let him have faith in you or someone he trusts for everything. All these are basically of religiousness, be whatever religion it be. And finally, once he is mature enough, he himself will understand God.