Start them young.
The earlier they learn to change tires, the better off they'll be. Flats will happen, so make sure your grom is carrying a spare tube when they head out to explore the trails with you. Made by Kenda for wholesale giant Quality Bike Products, Q-Tubes' Presta Kids' Bike Tube will fit inside a kids 24in mountain bike tire, and as its name suggests, it comes with a 32mm Presta valve. Carry one or two of these to show them that a flat tire doesn't have to mean it's time to head home.