Teach him how to thread the sewing machine for sewing and for bobbin winding - while it is off, of course. That will help him feel competent and accomplished.
I let my then 6 year old nephew push the foot pedal while I sewed, and he loved it. At the time I had a 1970's Kenmore mechanical that you could lift the top up to watch the gears move. That's what he really liked about it.
You could probably let him push the pedal while you actually wind the bobbin.
I like his sewing table, by the way. Clever idea and just right for him!
Enjoy!