2 Answers

them him  you'll give him a cookie or  3 M&Ms if he keeps the seat belt on . It'll work. Tell him to NOT tell the other kids, or you won't give him the reward. It's just your and his little secret

Frankly I think the best solution for your situation is to tell the parents that the next time there son refuses to wear his seat belt on your bus, will be the last time he will ride your bus. Period. Certainly you should be able to get backed up by your school administrator or employer -

If there should be, God forbid, an accident and the little stinker gets hurt because he isn't wearing his seatbelt, You and the school and possibly the department of education as well as the department of transportation involved in your town, city, county, state - will ALL be lined up for a high dollar attorney to hire to fight for their money, jobs and anything else in the lawsuit that the disgruntled parent will certainly slap on all involved!!! 

Put the little bugger OFF your bus - after you advise the parents that he is endangering the other children and you by not following the rules and disruption caused by you having to stop and pull over to re-belt their son back into the SAFETY of the SEAT BELT. 

INSIST the parent/parents come and pick him up from school BEFORE your time to take him back to where you picked him up in the day.  Best of luck to you. I wouldn't fool around with this, legally or otherwise, he could actually be the cause in a very negative future accident....