Re: youth ATV vs. off-road go-kart?
The go-cart will require much more flat, smooth open space. The ATV will get along better in any area. The go-carts you see sold at most stores (Walmart, Lawnmower Shops, etc.) typically have no suspension and lack power. They are more for a recreational ride, and not much for sport. If you're serious about a go-cart, you really want to look into buggies. These are go-carts with 125cc, 150cc, 175cc, 250cc off-road engines (like ATVS and Dirtbikes). They have a full suspension, disc brakes, roll cage, etc. But then you're talking more about an adult toy.
It sounds like you're really looking for a quad.
Another note: Youth ATVs will hold their value far better than any go-cart.