3D stuff isn't good for young children's vision.
While 3D video images are the latest selling feature of entertainment, it's not ideal for everyone. Sony has now updated its terms of service with the appropriate warnings relating to the PlayStation 3's new ability to support 3D displays. It reads:
Some people may experience discomfort (such as eye strain, eye fatigue or nausea) while watching 3D video images or playing stereoscopic 3D games on 3D televisions. If you experience such discomfort, you should immediately discontinue use of your television until the discomfort subsides.
SCEA recommends that all viewers take regular breaks while watching 3D video or playing stereoscopic 3D games. The length and frequency of necessary breaks may vary from person to person. Please take breaks that are long enough to allow any feelings of discomfort to subside. If symptoms persist, consult a doctor.
The vision of young children (especially those under six years old) is still under development. SCEA recommends that you consult your doctor (such as a pediatrician or eye doctor) before allowing young children to watch 3D video images or play stereoscopic 3D games. Adults should supervise young children to ensure they follow the recommendations listed above.
The warning of young children and 3D echos that of research relating to developmental vision.
Nintendo also told Kotaku that children younger than seven years old should be kept away from the 3DS' 3D mode.
Aside from the 3DS, which doesn't require glasses, an easy way to keep young children from viewing the 3D image is simply to keep the glasses in a safe place away from them.