He/she will have their license suspended and probably have to attend traffic school. Get ready for some BIG BUCKS in regards to the fine and court costs. And be sure you are sitting down when you get that letter from your insurance company..YIKES!
The courts or motor vehicle dept will suspend the drivers license for probably 6 months to a year or possibly until they turn 18, your insurance will probably increase tenfold, if they don't attempt to drop you due to the child being on your policy (it sounds extreme, but they do it.) As for the child, I'd hope the parent would teach them a lesson, if they are driving 70 in a 25, especially already having been pulled over for speeding, they don't deserve to be driving.