The 3d can be turned off and password protected on the 3ds. My boys both prefer the 3ds xl and my nephews 3ds....ds2 who had the 2ds won't really play it for some reason lol but it does have the advantage of being chunkier,not so delicate and you haven't got any hinges on it to break.
My boys have been using a ds of some sort since they were 3 so definitely age appropriate