Children should be seated in restraints that are designed for their size and body weight. The probability of children ages 1 to 7 being injured in a crash or sudden stop is reduced by about 70% when an appropriate child restraint is used instead of a seat-belt only.
Download: https://www.grsproadsafety.org/wp-content/uploads/GRSP-Child-Restraints-Fact-Sheet.pdf
Source: GRSP Seat-Belts Fact Sheet