I taught my 2 boys and 2 girls to sew as well as my youngest son's best friend. They all still do simple repairs on their cloths. My youngest daughter does more sewing when she has time (she runs a business). My son's friend is into Renaissance fairs and he makes all of his own cotumes. He is this big strong guy so many people are surprised.
The best way to teach is to start with paper with no threadin the machine. I drew straight lines, stars, large circles , etc. to get them comfortable with guiding things through the machine.
He will have lots of great memories of his grandma in years to come.