Check out www.Discgolfcenter.com They have a nice Pro D Hawk 163 g Blue, and a 148g Pro D Cyclone.
I would say stick with base line plastics, they are easier to throw.
If you do some online research you might be able to find a 130 esp Buzz I know I saw them before they were some sort of fundraiser disc, and they were in ESP going for like $5 or so.
I have also seen some 100g and 150g magnets on eBay. You just have to keep and eye out for them
But I think a Cyclone, Hawk, Magnet combo might be just perfect for a young kid.
Nate Doss Said "My dad gave me a Pro D Hawk to start throwing when he was 8 and he has had one in his bag ever since"
Ron Russel said "He world Championship to a Cyclone."
And Scott Stokley Says, " The Magnet, The best putter ever made, It's what he uses, its what everyone uses."
If he starts out with those three discs maybe he will be a World Champ one Day.
good Luck. I hope he really enjoys the sport.
I came across a 3 disc set at Fred Meyers, sure it wasn't Innova, nor Discraft, but it had the basic 3 discs, a driver, mid and putter, but they seemed from what I could tell, a bit smaller, for smaller hands, they were packaged so I couldn't actually get the feel of them, but this is something I'd recommend, it was $12 for the set.