I'm putting my kids on the bus to school for the first time. My 3 year old weighs 28 pounds and my 5 year old weighs 34 pounds. The bus company says kids over three don't need a car seat. Parents can purchase this seat http://www.unityparts.com/pro-tech-iii-without-pouch/ if they want (and for kids under 3) and they won't allow car seats. Do I really need to buy two hundred dollar car seats or is the bus company correct that kids over 3 don't need a car seat?