Ok, it's been a while since I've played Runescape and they updated their account creation thingamajig. Holy stuff, thingamajig is a real word?
What Runescape does is not ask for your email unless your age is over 13, which is told to them by an age box. If you are under, they tell you to put in your PARENT'S email. Abusing a loophole? Probably. Legal? Yes. Because they are not asking for YOUR email, they don't have to worry about COPPA.
You, however, do ask for email and have no age system. You have to worry about COPPA and you have violated it.