Don't mean to offend, but tell your kids the truth!!
There is no Christian God, Islam God, Budda, Vishnu etc etc...
These are all stories made up by bronze age sheep herders to explain away things they could not explain, and/or get control of people they wished to dominate or use.
Powerful people throughout history used these religious cults to their advantage ie. Romans, to control their populations.
It is still happening today, ie. Bush and the evangelicals, the Muslim fanatics etc...
Tell them the truth! Or at least tell them you don't know and let them decide when they are old enough and have ALL the information.
Indoctrinating children is a very BAD thing!