I always swore that I would never show my kids the prequels. Once you’ve watched them they can’t be unwatched. But eventually I relented, I figured if they were going to see them it might as well be at an age when they can really appreciate them (as much as it’s possible to any way). Your son seems like he might be at that age to enjoy the “humour”.

A good order to watch the movies is 4, 5, 1, 2, 3, 6. This keeps the saga framed in the OT and uses the prequels as flashbacks. It allows the OT to stay pure and unspoiled (mostly) while finishing on the high note of Jedi rather than the low point of Sith.

Then move on to The Force Awakens from there.