A child who has outgrown the internal harness or height limitations of a forward-facing child safety seat. Within the range of 40 to 80 pounds but under 4’9”. Within 4 to 8 years of age and is at least 35” tall.
http://safeseats4kids.aaa.com/faqs/when/when-is-my-child-ready-for-a-booster-seat/
Don’t Skip a Step. 1  A child who has outgrown the internal harness or height limitations of a forward-facing child safety seat. 2  Within the range of 40 to 80 pounds but under 4’9”. Within 4 to 8 years of age and is at least 35” tall. A child who cannot sit with their back against the vehicle seat with their knees bending at the edge of the seat cushion without slouching. A child who does not fit properly in the vehicle belt system.
http://safeseats4kids.aaa.com/faqs/when/when-is-my-child-ready-for-a-booster-seat/
8 - 12 Years. Keep your child in a booster seat until he or she is big enough to fit in a seat belt properly. For a seat belt to fit properly the lap belt must lie snugly across the upper thighs, not the stomach. The shoulder belt should lie snugly across the shoulder and chest and not cross the neck or face.
https://www.safercar.gov/parents/CarSeats/Right-Seat-Age-And-Size-Recommendations.htm
3. Booster Seats. 1  Once a child reaches 4 years of age and weighs at least 40 pounds, she can move to a booster seat. 2  A child is required by law to use the booster seat until she is 8 years old or 4’9” tall. 3  Both backless and high back booster seats are available.
http://www.nationwidechildrens.org/cirp-child-passenger-safety
Older kids get weighed and measured less often than babies, so check your child’s growth a few times a year. Generally, kids need to use a booster until they are at least 4 feet 9 inches tall and weigh between 80 and 100 pounds. For most kids, they will be between ages 8 to 12 years old. Talk with everyone who drives your kids so they understand that booster seat use is a must when your child is in their vehicles.
https://www.safekids.org/safetytips/field_age/big-kids-5%E2%80%939-years/field_risks/booster-seat
4 - 7 Years. Keep your child in a forward-facing car seat with a harness and tether until he or she reaches the top height or weight limit allowed by your car seat’s manufacturer. Once your child outgrows the forward-facing car seat with a harness, it’s time to travel in a booster seat, but still in the back seat.
https://www.safercar.gov/parents/CarSeats/Right-Seat-Age-And-Size-Recommendations.htm
Hard Facts. Children seated in a booster seat in the back seat of the car are 45% less likely to be injured in a crash than children using a seat belt alone. Top Tips. When your child is seated in the booster seat, make sure the lap and shoulder belts fit correctly.
https://www.safekids.org/safetytips/field_age/big-kids-5%E2%80%939-years/field_risks/booster-seat
If all back seats are occupied by. children under 4, then a child under 4 may. ride in a car seat in the front seat. A child in. a rear-facing car seat may only ride in the. front seat if the airbag is turned off. Children to be properly buckled in a car. seat or booster seat until they are 8 years. old or 4’9” tall. Children must ride in a seat. until they reach the age requirement or the. height requirement, whichever comes first.
http://www.michigan.gov/documents/msp/booster_flyers_361887_7.pdf
4. Lap and Shoulder Seat belts. Most children are ready to use a lap and shoulder seat belt without a booster when they are about 4’9” tall. Children are required by law to be secured in a child safety seat or seat belt until they are 15 years old.
http://www.nationwidechildrens.org/cirp-child-passenger-safety
Once a child reaches 4 years of age and weighs at least 40 pounds, she can move to a booster seat. A child is required by law to use the booster seat until she is 8 years old or 4’9” tall. Both backless and high back booster seats are available.
http://www.nationwidechildrens.org/cirp-child-passenger-safety
what size does a child have to be to move to a booster seat
The size of a child has to be to move to a booster seat is at least 4 feet 9 inches tall and weigh between 80 and 100 pounds. A child has move to a booster seat at least 4 feet 9 inches tall and weigh between 80 and 100 pounds. To move to a booster seat the size of a child has to be at least 4 feet 9 inches tall and weigh between 80 and 100 pounds.