During the school holidays it's so easy to fall into the trap of waking up late, watching Tv for ages and doing minimal physical activity.
First of all, take the kids to the park. Make it fun and google search parks in your area and go find local parks you've never been to. Gives the kids new scenery and bring a ball, bike or frisbee and don't stop until you're all exhausted.
Second of all, plan physical activity outings for the holidays. Take your son and his friend to a bike riding track for a few hours, go bowling with your neighbours, hit up the local tennis courts with your kids and practice.
Third of all, use your own resources. If you have a trampoline, basketball ring, ball or soccer net at home then use those for exercise. Join in with the kids on the trampoline, it'll be more fun for them.
Fourt of all, go walking during the day or at night as a family. Visit a friend, get friends to join as well or go for a healthy picnic at the park.
Last of all, sign up the kids for a sporting team. Football, tennis, karate, anything that gets them moving.