From
BloombergNintendo Co. will bar children ages 6 and younger from using the 3-D functions of its new handheld game machine at an introductory event for the device.
“Looking at 3-D images for a long time may harm the growth of children’s eyes,” Nintendo said in a note to visitors coming to the event next month, posted on its website. The company’s new 3DS players will be promoted at the three-day event in Chiba prefecture, near Tokyo.
They also say you should take a break every thirty minutes whilst playing it. I'm still getting one, unless they have a stupid price point to start with.