A lot of us are out west, but there may be a few easterners on here.
Boatertalk.com seems to have a bigger set of east coast paddlers.
My daughters are 14 and 16. I had them in hardshell kayaks at 6 and 8, and they both had rolls. Got them in whitewater too early, and they got scared, and haven't kayaked since. Both love to raft, and I took my 16yo on the Main Salmon a month ago and she LOVED it.
Safety: really depends on the water. Whitewater kayaking is a social activity; not really safe solo, so the safety also depends on the safety attitude of your crew. Safety is relative...your son is probably safer doing this with you than running around town with hooligan kids without you!
Find a couple of whitewater kayaks for you and your son, go play in the warm late summer water, and look for some pool sessions this winter to work on your roll.
A swiftwater rescue class is also a very good idea.
From there, just find some local boaters to tag along with and some Class II whitewater to run and get comfortable on.
Welcome to our passion!