:nod::nod::nod:I'd say as soon as they are able to communicate. I see no good reason to lie to children. The amount of truth you tell them depends on their age, though. If a little kid wants to know where babys come from, for instance, there's no need to give them the full, detailed, birds and the bees talk, saying a baby comes from mummys tummy is enough for the time being and a child will be satisfied with that answer till the're older.
im surprised at how high in age some people said. for me, its started at birth with Jace :shrug:
a childs understanding of things are taken for granted. they are sponges and soak up alot more than what people give them credit for