Great question! It’s never too young to work the core. Many good core exercises for adults are based upon developmental postures and movements which kids typically automatically spend time in. Recognizing these movements and creating games and challenges to utilize them allows for integration of nervous system development as well as local strengthening to the “core”.
For instance, movement in a “bear walk” is a developmental progression from crawling. We exercise adults in quadruped (all fours like crawling); kids do well with walking on hands and feet (just pick up your knees from an all fours position). Set up a course around the yard or living room and see who is the fastest “bear walker”. Weight bearing on the arms encourages development of scapular control, and the reciprocal pattern of the walking movement is great to activate the diagonal muscle systems of the front and back of the core.
Also, kids love to hang on things, their innate body weight to strength ratio is quite impressive when compared to a typical adult. When supervised appropriately, one can sometimes trick them into doing core strength on the monkey bars or rings at the playground. Challenge them to see how long they can hang with their knees tucked up towards their chest (as if they were sitting in a chair). This posture mimics the most initial stage of core stabilization we ever achieve as humans, the typical position of a 3-4 month old infant lying on his back playing with his toes. At this time, the infant has activated a perfect breathing and core stabilization pattern. This great early core exercise then utilizes the same muscle pattern against gravity when hanging from a bar or rings. For kids as young as two, set up a low set of rings (Ikea sells a safe but inexpensive set) over a soft surface and count how long they can hold a tuck hang.
Keep your kid’s core strong from the start and, hopefully, you can ward off some of the weakness we all develop as we are overtaken by our chair dwelling society. The Dynamic Neuromuscular Stabilization (DNS) program at www.rehabps.com provides a much deeper look into developmental postures and exercise.