Hmm 5 year olds....
How is she in her logical an critical thinking?
Depending on the answer, you could go with "Well,
I don't think he exists, since I've seen no evidence for him. But don't take my word for it, always investigate things for yourself!"
OR
"No one really knows, honey (see, I'm being a kind parent here), I don't think he does, but others do. Perhaps we should speak more about this when you're a little older."
Also, I'm very interested in what response religous folks would give. I have my suspicions, but will keep them to myself for now.
I hunt for the truth
I am the one Orgasmatron, the outstretched grasping hand
My image is of agony, my servants rape the land
Obsequious and arrogant, clandestine and vain
Two thousand years of misery, of torture in my name
Hypocrisy made paramount, paranoia the law
My name is called religion, sadistic, sacred whore.
-Lyrics by Lemmy Kilmister of Motorhead