a bit naive or a bit dim?
I'm neither a troll nor 2bubs4me so no hunting. 
I dont remember ever believing in Santa, and I remember quite a lot from my pre-school years. I knew the size of the Earth, the number of people and the impossibility of the logistics of 'Santa'. I also knew better than to beleive everything my parents said
.
My DS is basically the same. I understand that 3yo's believe - it's cute, but I think it's a bit creepy when 8+yo's still do.
But I would never actually criticise a parent for having such deluded sheltered DCs.