Agree with you Roseway, (although |I can't see why parents can't prize the device off them ) For once no one seems to be screaming about Strontium 90.
To provide a bit of science, the practical limit was 10mw/cm^2 = 100w/m^2 which was known to cause eye damage, a thermal effect. ( half that would light a neon bulb !)
The long term limit is much less than this, ? 0.1 mw/cm^2 to cover possible non-thermal effects. AFAIK no such effects have been proven.
To put this in perspective the sun can give 900 w/m^2 but that is "Natural" so it doesn't count !