better yet, PRP Seats - Custom Off Road Racing Seats also makes a Preemie seat thats even smaller. I have owned both the preemie and the pre-teen so let me tell you my advice.
At 2 years old your kids still need good support. The seats while they look and work great aren't quite like a car seat in that they hold them in really tight. Even the 4 or 5 point harnesses aren't real great because it hard to get them as tight as they should and fit as properly as they should. Now I am sure you wont be mashing the gas with your kids but think of their heads and how they bobble. My advice to you is to get the Pre-Teen seat and then run a small kids car seat or booster seat in it. This was the best way to haul my young kids that I found. Then as they grow out of the booster seat they can sit comfortably in the Pre-Teen seat.
Under 2, stick with a standard car seat (you can use ratchet straps to secure it to the suspension seat). Much safer for the little ones. Over 2 1/2 or so, get a Preemie booster with no tabs.