When they're old enough they ought to be able to find out for themselves. You can furnish them with a copy of the Magic of Reality when they're about 12.
I don't think atheism particularly excludes the possibility of there being something like a God or an afterlife so it's better to avoid make definitive claims.
I don't think atheism particularly excludes the possibility of there being something like a God or an afterlife so it's better to avoid make definitive claims.