Q: I saw a father and son in the gym today, the son was probably around 7 or 8 and he was doing a few exercises with weights so I was wondering what is the deal with kids and weight training? What is the recommended age for kids to start exercising with weights?
A: aaah always a fun one, especially when parents ask me this. 
The rule of thumb is additional weights only after age 10 and older (preferably older) and machines (gym equipment) only later in teens, and I feel very strongly about this!
A child’s body and particularly their bones are still developing and when you add unnatural external weight like dumbbells and machines (I’ll get to this in a second), you can actually hamper proper development! Not worth it! When it comes to gym equipment, these are ergonomically designed for an adult body. Our proportions are so different to that of a child (here is where my hubby would stop me and say, well, some children are taller than you babe, blah blah, insert eye roll), back on point. This means that those machines are doing more harm to that little body than good. They are designed for adults, not children. The weights are too heavy and the distances from all the seats etc are all wrong. A child should definitely NOT use any these machines.
What a child can do is body weight work, natural movements like cycling (if someone sets the bike up correctly for them because incorrect settings on bikes can cause knee damage and all sorts), yoga, stability ball training, beach or sand work, speed and agility work. No additional heavy weights just their own body weight.
I have two very active children, my daughter in particular loves training with me. I have to watch her like a hawk because if I turn around she is picking up medicine balls and 5kg dumbbells or flipping quadbike tyres. I don’t encourage it! Body weight work absolutely, and natural movements all the way. No weights, no machines!
Many parents get upset with me when I tell them this, or when I refuse to use weights with younger clients. It just isn’t worth it folks, the long term damage to your child’s body, along with increased potential for injury later in adolescence and adulthood is just too risky! Let them develop naturally, there are many many ways to keep your child fit and active (even when they want to improve their sports performance) until the age of 10 and older if they can hold out!
