Rat,
Three months ago I bought a Bombardier, Traxter Max 650. It is the largest two person ATV that Bombardier makes. Mine is what they call the XT model, comes with a winch, brush guards on the handlebars, and "radial" tires.
So far I've put 420 miles on it, all off road/trail riding in the Rocky Mountains.
My reasons for this particular model; it is made specifically for two up riding, passenger has raised seat area with raised footrests and grabhandles also a padded backrest, 1100 lb. towing capacity, large 8 gallon storage area in the front (works great as a cooler for picnics), radiator is in the rear so no engine heat and doesn't get full of mud or rocks, bullet proof Rotax engine, also has great engine braking for slow/controlled down hill creeping, hardly ever use the brakes.
I took it Elk hunting for 9 days the first week of November, in camp were about 12 other various makes of ATVs. Second day we had 6" of snow, no problems. Rest of the week we had 4" of mud, no problems. I was able to go everywhere the other brands could go, and a few places they couldn't. The longer wheel base means it takes a little more room to turn, but this was never a problem - it also makes it a lot more stable on steep climbs/descents.
I would recommend that anyone who wants to ride more than one person, take a serious look at these "two up" ATVs. Your 3 year old wont stay little very long, then where do you put him? Bombardier makes several models of 2 person ATVs, including a gear drive - auto/manual shift, one which is convertible for one or two people, and has one of the best 4 wd systems in use.
Also if you want to keep the ATV in the tractor category, John Deere is selling rebranded Bombardiers that will match their tractor colors.
I have a small daughter, my wife and I have ridden some easy trails with one of us driving, the other on the back, with our daughter between us. Taking it real easy, great fun.
I have friends that have the padded add-on rear seats so they can ride a passenger on their regular, one person, ATVs. While this gets them by for easy trails, the short wheelbase with the passenger sitting over/behind the rear axle, is pretty dangerous if attempting any steep ascents/decents.
These models are a little pricey compared to some of the other single person models, but the additional price is more than offset by the added versatility and safety.
Hope you find a Zooter that everyone can have good safe fun on, good luck.
DT