- A child is safest in the child safety seat that fits him best. A child under 40 lbs. usually fits best in a five-point harness car seat. Once the child has exceeded the weight limit of the car seat, though, he must be switched to a booster seat. Another consideration is the height of the child. If his shoulders are higher than the top strap slot in the five-point harness seat, he is ready for a booster seat.
- Children need to be in booster seats until the regular seat belt fits them correctly. For most kids and for most cars, this will be when the child is about 4 feet 9 inches tall. The shoulder belt must lie flat across the child's chest, and should not slip off her shoulders nor rub against her neck. The lap belt should go across her hips, and should not ride up on her abdomen. Finally, her feet should touch the floor of the car without her slouching down.
- The seat belt must be threaded through the booster seat correctly. Refer to the owner's manual that came with the booster seat. Only use a high back booster if the child's ears are above the level of the car's headrest when seated. A low back booster will not offer any head protection, and they are only safe to use when the car's headrest is tall enough to support the child's head and neck. The seat belt should lie across the child's chest, hips and thighs. If possible, try the booster seat in your car before purchasing it to avoid buying a seat that does not fit well.
