My son recently received the Radio Flyer Pathfinder wagon as a gift. It's a plastic Radio Flyer wagon that seat two children. The wagon is very sturdy and pretty roomy. One of the pictures I posted shows my 8 year old nephew and my 2 year old son sitting in the wagon. Both are somewhat tall for their ages, so if you have small children, you could probably toe around 3 at a time (though there are only two actual seats with belts).
The two seats face each other, and have seatbelt to keep wigglers in (unless they no how to unsnap the buckles). The seat backs fold down to leave a flat wagon bed, allowing kids to pile their toys inside for a ride. The seat backs can also be done with one up as a seat, and one down for storage.
The wagon looks like a classic Radio Flyer wagon, except that it's bigger and pastic. Even though it's very sturdy, it's still light enough for a toddler to pull around, if it's not too loaded up with toys! This is one of my sons favorite toys and well worth the price (ok...we got it as a gift, but it would have been worth it to pay it!).