Strong core muscles give you that nice, flat post-pregnancy tummy, but they also help your child build strength. Kids that don't have strong core muscles often get tired or worn out easily, according to occupational therapist Jill Howlett. You can beef up your kids' tummy through play. Young children can do exercises just using their own body weight or toys, and they won't even realize how hard they are working.
The classic wheelbarrow game will let your kidlet work her core muscles without even knowing it. Grab your child by her thighs while her hands are on the floor. Help her walk on her hands around the room. As she grows stronger, you can grab her by the knees, calves and then the ankles. According to Howlett, you can work up to stair climbing in the wheelbarrow position.
You can use balls for so many types of core exercises. If you give your child a ball big enough to roll on, he'll slide over it and bounce on it, working his core muscles the whole time. Encourage him to put his feet on the ball and his hands on the floor, like he was doing the wheelbarrow, to further improve his muscle strength. Just make sure to use a ball designed to hold weight. You can find exercise balls in different sizes that will hold even the most vigorous bouncer.
You might remember these from gym class -- they are flat boards with wheels underneath. Some of them have four wheels but others are less stable and require more balance, with just three wheels. Let your child scoot around on her stomach. She'll be using her core muscles as she keeps her balance and holds her head up.
If you want to encourage core development at a more focused level, you can do a child-style workout for the abdominal muscles. Have your child make a bridge while he is laying on his back. Keep the shoulders down -- he probably won't have the balance to go into a full arch -- and his tush way up in the air. Support him while he lifts one leg and then the other. While laying on his stomach, have him lift his legs and arms into the flying "Superman" position. According to HealthyChildren.org, your child should do 10 repetitions of each exercise.