At that age, whatever they get, it'll be obsolete by the time they leave home.
Laptops are roughly double the price, probably four times the price to upgrade or fix, and don't last any longer. They are also much more fragile, and I know how much my kids looked after things when they were in their early teens.
So, my opinion, for what it's worth, is go chequebook in hand, to your local "big name" PC distributor (PC world, dixons, etc.) and say you want three identical games-spec PCs, and are not spending a penny more than absolutely necessary.
I did something similar about a year ago when my, Mrs.G and G.Jr all decided we needed new PCs - got three high spec machines (admittedly without monitors) AND a 3-year on-site warranty for £350 each from PC World. I'll admit that Packard Bell isn't necessarily the best make in the world, but it's good enough, and when 16Yo G.Jr decided to upgrade his PC himself without consulting anybody and fried the motherboard a few weeks ago, the warranty people sent somebody out to replace it free of charge (and did his upgrade properly whilst here) in about 4 days.
That said, if you are set on Laptops, I've had a couple of desktops and a laptop over the last few years from
here and the price and initial service have been excellent. After-sales has been pretty reasonable - although not necessarily world class.
G
Secretly agreeing with
Binoculars.