OK Grandma, he wants to sew, let him but make sure its something he can take pride in showing off - not just a piece of fabric.
Boys like treasures, so lets make him a little drawstring bag that he can put all his tiny treasures in (marbles, hot wheel cars, little army men, superheroes, etc) Measured about 5X7 finished. Boys love that stuff.
A oblong piece of felt is perfect, Let him stitch around three sides and run a shoestring around the top for closing. He can sew by hand or you can guide those tiny fingers on the machine. Over the years I've held 4 granddaughters on my lap while they "sewed on Nana's machine"
Have fun, enjoy the time