The new safety notice was spotted by Reddit user KGrizzly. It warns about symptoms that some people experience, that you should make sure the area around you is clear, and that "the VR headset is not for use by children under age 12."
Meanwhile, the Oculus Rift's documentation says that the headset shouldn't be used by children under the age of 13, while the HTC Vive is a bit more open-ended, simply stating that "the produce was not designed to be used by children." It adds that older children using the headset should be monitored by adults.
Sony is expected to announce a release date and price for the PlayStation VR at next week's Game Developers Conference.