This thing is called a Scuttlebug. It's like a hybrid scooter/ride-on toy/pedal-less trike...whatever it is, it is apparently very, very fun!
I was looking at three wheeled scooters as Matthew wouldn't leave his sisters' scooters alone, but I couldn't see him having the coordination to use those yet. Most ride-on toys are pretty babyish and seemed like they would have been a better purchase for last summer. And then I ran across this style of three-wheeled pedal-less ride-on toys - they seem like a nice compromise for a nearly two year old who thinks he's big!