I still believe that ‘actual weights’ should be avoided until the child is able to do the absolute basics of bodyweight movements - push ups, pull ups, crunches, squats, lunges, etc. with good form. There probably isn’t anything wrong with having your son start with actual weights, but you will need to tone down the weight of them a lot for them to be appropriate… Even with your son weighing about 80lbs, a barbell alone weighs 45lbs - which is a lot in the scope of relative strength.
Why not try giving him a bodyweight exercise circuit, or perhaps a few circuits done throughout the week and see how he feels about it then? This is what I have my daughter do:
Mon, Weds, Fri
Progression Method: Monday = 2 rounds, Weds = 3 rounds, Fri = 4 rounds. At the end of the week, increase reps +1 and start over at 2 rounds.
-Push Ups x5
-Sit Ups x5
-Bodyweight Squats x5
-Flexed Arm Hang to Failure (timed, to be replaced with pull ups when capable)
-Clean Press x5 (with faux bar, haven’t integrated this yet but plan to)
-Tues, Thurs, Sat I have her work on gymnastics skills, floor, bar, beam, etc. so no strength training these days.
-This is all supplemental to the 3x per week we have her in gymnastics class
Expect to be underwhelmed with performance lol (I was, and frequently am), kids just need lots of encouragement and low standards on form/effort from you. If your son is truly interested - he will ask to do it again, but anticipate that you will need to encourage him to continue doing it with you.
P.S Yes, I have my daughter do a lot - but none of this is my wife or I pushing her to do this; she just really loves gymnastics and I’m glad I can help her with that.