...A person's spiritual condition, it seems, is much like the condition of a patient with systemic sclerosis. While all humans are born sinful, children have less of the pollution and less of the hardening of adults. While the extent of our depravity cannot change, for from the moment of conception it encompasses all that we are, the degree will and must change. Life without God progresses much like the disease. It causes increased hardening. What was once soft becomes hard; what was once supple becomes stiff and stretched. The longer a person denies God and the more his internal pollution increases, the more hardened he becomes against God and against His gracious offer of salvation. No wonder the Bible is filled with commands and exhortations that as parents we dedicate ourselves to teaching our children what God requires of them. And what impetus this should give us to obey Him! ...
Quote taken from Two Great Barriers to Faith.
A reasonable response to those who suggest coversion the number of children/youth conversions is simply the result of brain-washing.
(Note: Several other factors come into play, such as the fact that some may proclaim faith when they are not actually saved; there is an blessing associated with growing up under believing parents, etc.)