Don't use Google+, it's simple.
There are more laws than I can count preventing under 13s from using such sites. Nevertheless, COPPA is still applicable here. Online laws are enforced dependent on the owning company's location, so Google can be held liable for anybody you register. Realistically, they probably shouldn't have Google Apps accounts until the reach 13, but I'm sure we can make an exception there, considering google doesn't even ask for age until G+
You could also get COPPA forms for the whole of year 7, and send google a nice big parcel of COPPA Consent forms, but they might prefer to just turn down your business than have their legal team crawl through it all
