[NickH]

Three -

I too was a competitive swimmer and coached. At your sons age, core strengthening will be very valuable. Also, I'm not sure kicking against the wall is the best exercise. It does not give him a "feel" for the water, as though he were swimming.

Other options to consider, beyond what has been recommended already:

squats, lunges, leg presses, etc. -- Use lower weights and focus on repetition at his age.

Also, Medball work outs are a grea way to build strength. There are many interactive exercises you can do with him that will help build strength, keep it interesting and give you a work out too.

Also, look in to water training tools. Rather than having him kick against the wall, look at resistance/"drag" suits and cords/tethers. These will allow him to do kick drills and build up the leg strength. They can also help with overall strength. The tethers I felt were most effective were the rubber bands that allow the swimmer to swim but provide greater resistance w/ distance. They can be fun too.

Hope this helps. Good luck!