The machine translation is a little rough, but the gist is clear: Nintendo has issued a warning that kids under six shouldn't use the 3DS's 3D mode because their vision is still "in the development stage," and the way that stereoscopic 3D works, delivering different images to each eyeball, "has a potential impact on the growth of children's eyes."
Sony's also noted that kids under six shouldn't play 3D games without being examined by their eye doctor first. But the 3DS is in a slightly different position than the PS3, since Nintendo's way more geared toward kids than Sony is.
To keep the childrens away from 3D, the 3DS will apparently have a parental lock on 3D, locking the 3DS in 2D mode. Even with the parental lock, though, this is pretty crazy. Nintendo issuing a warning explicitly stating, "Hey, our product could screw up your child's vision." Who's gonna buy that for their kids?