Whatever you do... tighten every nut and bolt before they ride it.
I got a Panther 120 (I think) for free, when I bought my toy hauler. My kids wanted to test drive it. I said no. They bugged and bugged me. So I caved. They all have their own machines so I saw no reason for them to ride it. 2 laps around the house each. 8 laps later I was missing about 25 bolts and misc nuts. Even the axle nuts were spinning on the axle and the chain fell off. What a POS!
I bought a little Yamaha raptor 80 for my kids. It's gone through 3 kids now and I haven't even changed the spark plug yet. Just a thought but going with a brand name has its perks. A little more up front, no maintenance and BIG resale value. My kids all started riding it by 4. I hate pulling wrenches all weekend while camping.
go with the pitster they are well built and have a 1 year warranty and the parts are available with in days, getting the grandson the 90 quad no reverse but they only cost 1200.00