Let's be honest, there is a big difference here - everyone has realised about FC by the age of 10, but not everyone who believes in god as a child stops believing in it as an adult. FC is a harmless childhood fantasy like the Tooth Fairy (and I think DD, who is 7, has twigged about that one!)... and FC doesn't require people to give up anything, lead their life in a certain way, worship anything, etc.
With god, there's more than the simple question of belief or non-belief. There's all the baggage that goes with it about the Christian way of life, worship, etc.
I personally can't "prove" god doesn't exist. Contrary to the views of some theists, that's not a weakness in my argument - it's simply a philosophical impossibility. You can't prove the non-ness of something. And, to return the favour, I don't usually challenge Christians to "prove" their god - I appreciate it isn't possible to do so in terms I would necessarily accept. But neither they, nor I, can prove or disprove Thor, Apollo, Ra, Father Christmas or the Tooth Fairy... doesn't mean we should necessarily believe in these things. You have to look at how likely these things are.
If I admit to the 0.001% possibility that god might exist, that's nothing like enough for me to live my life as if it does. I'd need 50% at least before I'd take a punt. There is no way anyone could ever demonstrate 50% to me. And even if I were to believe - a huge leap, and one which would involve me deliberately choosing to leave behind my faculties of critical reasoning - that only takes me to the point where I'd accept this thing exists. It would then be another huge leap across the logic chasm to establish that this thing is somehow worthy of my "worship". I don't do "worship" - I find it a very unhealthy mental attitude.