When they're exempt for medical reasons
If you have adult passengers, it's their responsibility to wear a seat belt, but you should still remind them to use one as they get in the car. It's your responsibility to make sure that all children in your car are secured with an appropriate restraint. Exemptions are allowed for those with a medical exemption certificate.
B When they're under 14 years old
C When they're under 1.5 metres (5 feet) in height
D When they're sitting in the rear seat