My 3 year old (turned 3 in April) is tall and long in the torso. I don't know his exact measurements now, but he was about 39 inches in April. He outgrew his Roundabout, and is now in a Marathon in my car and a Regent in DH's car. We recently had our carseats checked and they said that in forward facing seats, the shoulders should not be above the height of the tallest slots. I checked the Marathon manual and it says that the carseat may be used after that happens, until the tops of the ears are higher than the seat. According to the car seat techs, in an accident he would move forward too much if the straps are coming from lower than the shoulders. Would someone please clarify? I was hoping to use the Marathon another year or so, at which point we'd get a Parkway or Compass.