How many times do you see a child does his homework without taking a lesson? Almost none. If you don't let him take a lesson, he will not do any related work, unless it's purely play. Chess is not pure play. Chess is play and work.
If he doesn't take lesson, doesn't do homework, will he go to tournaments? I can bet he doesn't even know where to find a tournament.
If he doesn't play in tournaments, how long can his interest last? From my experience, the longest might be 2 to 3 years, while the shortest is just a few months. When his interest is gone, he will slowly stop playing chess. When he grows older, he might realize, what a beautiful activity he has missed.
All these are starting from a chess lesson. So don't procrastinate. You never know your child's potential. He will surprise you again and again. You might have next Magnus at home.