Tricky answer. It depends really. In some contexts, children can get away with asking things, things that are rude, that adults can't. But children will be forgiven for not knowing better. It has to do with group membership and the idea that children, because they are still learning about the world, are not yet "complete" and therefore, not fully legitimate members in the social group. So for many, if a child questions certain things, such as the status quo of the group, the child is seen as overstepping his bounds because he isnt yet a "full member"
Cos some of us adults don't know how to answer or even the orrect answer so they tell the children off to save face.