re: Cutting down clubs for kids?

The weight may be too much for him.

I’m not a physics PhD, but all shafts have kick points, weight, and various characteristics that need to be fit to the players size and speed. The club head will be heavy for him as well.

US Kids is probably the best option. You can find decent used sets for various ages pretty easily online.

Ping builds kids clubs too.

Sounds like you two are spending quality time together and having fun. Having a full set of irons won’t change that. Learning to play with half a set might be good long term as far as discovering different ways to setup and swing various clubs to make different shots.