It's a good question, but it's incomplete.
Most of us have a preconceived notion about "weight lifting," often visualizing poorly executed heavy squats and bench presses. However, the real concern isn't the weight itself—it's the amount of force required for a given exercise.
For example, let's consider a 75-pound 8-year-old performing a traditional squat with a 25-pound weight vest. Generally speaking, there is 100 pounds of resistance (body weight plus external weight) that needs to be overcome. Each leg is absorbing and generating 50 pounds of force. Now compare this with the same child doing a single-leg squat with no external weight. The force required for that single leg is 75 pounds since the solo leg has to absorb the child's entire body weight. While admittedly this example is a bit over-simplified, it demonstrates how questions about appropriate external weight usage can be incomplete.
Furthermore, based on my experience with young children, I can tell you they often attempt single-leg and gymnastic-type exercises that require significantly more force than many exercises performed in a weight room.
A better question is: At what age can kids start training in a way that produces more force and makes them stronger? The answer lies in our biology. From the moment a child learns to crawl, they are learning to produce force. The same goes for walking, running, and jumping. For structured exercises like lunges or push-ups, kids can start as soon as they are able to understand and follow instructions properly. Of course, it's crucial not to apply force to the point where a child can't maintain the integrity of the movement—like having a child squat 200 pounds or jump off a 10-foot playground structure (though they sometimes do!).
With that said, I believe that resistance training should not be the primary focus for children under 12 (though it should be a part of their program). Instead, training should center around three core components: speed, movement competency, and reactivity. But that's a topic for another time—I'll break it down further next week!
