Charter rights in Canada can now be restricted determined by age.
Social media is a (the) major means of communication, self-expression, political participation, education, and association.
Preventing all Canadians under 16 from accessing those platforms restricts expression protected by section 2(b) of the Charter.
Thinking about it, it may also engage section 15 equality rights because it creates a distinction based on age.
Children under 18 can't get credit cards in Canada. So how & why can they get cell phones? Because a responsible adult usually buys it for them, sets up controls (or not), & pays the bills. The adult can set device access controls. They don't need (or want) the government. Next!