Don't tell him to follow you. Tell him to follow the tracks your skis make. Following you will be straighter down the hill than following your skis' tracks.
Try to discourage him from making power wedges straight down the hill. Encourage him to follow your skis tracks as you curve across the hill.
Find something each of you can hold between your ankles to learn to keep your feet together. A bone-shaped car wash sponge is one possibility.
3 things for kids...safety, fun, skills. Safety is always #1. And, if they don't have fun they won't learn skis.