#1 Have your son sit on your kitchen counter with his legs dangling down. Put your hand on the inside of his foot (the affected leg). Tell him to show you how strong he is by pushing his foot against your hand. You want to give resistance. Get him to push and hold for a count of 10. Do the other leg. Switch back and forth doing each leg 3-4 times.
#2 Have your son lay on the floor on his back. Bend the good leg at the knee and keep the affected leg straight. The foot of the bent leg should be next to the knee of the straight leg. Do a leg lift (help lift his leg slowly), keeping the knee in a locked position. He may not be able to get it up to a 90 degree angle. Take it as high as possible without hurting him. When you get to that point, gently hold for a count of 10 with slight pressure added. Then bring the leg down and do the other leg. Stretch each leg 3-4 times.
#3 Have your son lay on his tummy on his bed. Have both legs bent at the knees in a 90 degree angle-the feet will point straight up. Hold both feet in your hands. Gently point the left foot over toward the back of the right knee. Only go as far over as is comfortable (and don't let him rock his hip trying to go farther-keep hips flat). Hold for a count of 10. Bring back up and do the other leg. Do each side 3 or 4 times.