Bigger kites are much more stable in the air than smaller ones.
Small kites are much snatchier as they react quicker to inputs and fly faster through the air than big kites.
I started with a 3.4 Hq and eventually ended up with a 15m Flysurfer. The 3m was fun, but snatchy. The 15m is slow to turn, mostly predicable and generated crazy amounts of lift. Could easily jump 5m+ and drift nicely back to earth.
One of the easiest kites to fly with handles (that I had) was a 8m buggy kite. Was like an old diesel engine. You could fly it in low winds, but when the wind picked up you got nice slow, predictable lift. Could easily float 1-2m off the ground for over 10m with the board….
The scariest, most unpredictable kite I had was a 5m Blade. It flew so fast and turned so quickly. Would often find myself 4m up in the air and suddenly getting dumped. Only ever flew it on beaches (clean, steady wind) as it was a bit risky if the wind was punchy. Could build up masses of speed and tack sharply into the wind. Jumping with it was fun, but it launched you up so quickly you had to be on the ball.
For your son you should look at buggy kites. They don’t generate as much lift.
However, it has been years since I looked at a new kite. No idea what is available now.
Only take the Flysurfer out once or twice a year to Reschen Lake in Italy once it has frozen over.
Snow is best for harsh landings.