When I first started driving (1971) I tried to get everyone to buckle up because that was the "new but not enforced law" ... My mother refused to buckle up and told me I was being disrespectful (not as nicely said). I still buckled up but didn't require anyone else...fast forward 25 years...
DH didn't buckle up either.. UNTIL a close friend (young girl about our daughters age) was in a serious accident and told him that the only thing that saved her was her seat belt... after that we GOT into the habit... now, the car doesn't start till everyone is buckled....