I can check with Sony for an official response.
In the meantime, I can tell you that the Sony Children’s Headphones are rated at 90 decibels (dB), which doesn’t meet the NIOSH (National Institute of Occupational Safety & Health) guidelines for safe volume levels. Safe maximum volume level is 80 dB, 90 will incur damage after about 8 hours, and 100 dB, which is the maximum level for most headphones, will start to damage hearing after about 2 hours. Check out this chart to see when hearing damage starts to occur (http://www.betterhearing.org/hearing_loss_prevention/noisethermometer.cfm).
Also, the Sony Children’s Headphones are designed to fit children 8 and older and will not fit your child properly or comfortably. Look for a pair that limits the volume to 80 decibels and are designed for younger children. (If you are looking for decibel level spec, it’s usually referred to as “sensitivity” and noted as: 80 dB/mW)