For children under 6 years of age, exposure to stereoscopic 3D images could be detrimental to the eyes. Because of this, Nintendo are including a 3D lock feature in the Nintendo 3DS, using a PIN.
The report comes by way of Inside Games, who noticed the feature mentioned on Nintendo’s page for their upcoming Nintendo World event. With the 3D lock enabled, the 3DS will only display a regular image as opposed to the “popping out” 3D, and the effects of the 3D slider will be disabled.
There’s still a few things we don’t quite know about the 3DS, so hopefully the Nintendo World event will shed light on more of the system’s features.