All children riding in passenger motor vehicles must be in a federally approved child passenger restraint that is properly fastened and secured according to the manufacturer's instructions until they are 8 years old OR over 57 inches tall.
When children outgrow their booster seats (usually around age 8, but more importantly, when they are taller than 57 inches), they must wear a seat belt that is properly adjusted and fastened according to the manufacturer's instructions until the age of 13. Drivers found operating a motor vehicle with a child under age 13 who is not properly restrained may face a fine under MGL Ch. 90 Sec. 7AA.
Any person age 13 or older is required to wear a seat belt under MGL Ch. 90 Sec. 13A. Drivers may be fined for not wearing a seat belt themselves and for each passenger age 13 or older who is not properly restrained. Passengers age 16 or older who are not wearing a seat belt may also be fined.
Massachusetts is a secondary enforcement state, meaning that a driver may not be pulled over for failure to wear a seat belt, but they may be fined for not wearing a seat belt if they are pulled over for another reason.