Nintendo has publicly stated that the 3D mode of the 3DS is not intended for use by children ages six and younger, citing possible harm to their vision. Nintendo suggests that younger players use the device’s 2D mode instead, although the American Optometric Association has assured parents that 3D gaming in moderation would not be harmful for children. Nintendo has stated that a parental control involving a PINwill allow parents to disable autostereoscopic effects.
(researching Nintendo DS etc for possible buy for the boy. I’ve seen the XL model on ebay, bigger screen = bigger Mario = more fun ?)