My sister refused to fly for years, got sick on flights secondary to anxiety (but also flew mid afternoon on most flights adding to the TB B). Jokingly, I always asked if she wanted to "go up" as I would be heading out on a refuel mission always expecting a "no" or "hell no" response.
Surprisingly, one day she said she would meet me at the hangar (I thought she was pulling my leg) ... but low and behold, there she was. I went through the pre-flight with her showing her everything which relaxed her to know that the AC are dirt simple and fairly easy to pre-flight (it also helps that the Tiger has full engine access for new pax to see everything).
At engine start-up she was tense, but I told her we would/could abort anytime she chose. We taxi out to the runway only to see an RV do a slam and go (bouncing about 15 feet in the air) and she asks, "are we going to be landing like THAT!", I assured her we woud not.
Long story short, she relaxed as soon as we got to pattern altitude and was calm enough for me to leave the pattern. After 30 minutes, I suggested we return to land. She said she wasn't ready yet and wanted to go over to the Class C for a landing! It was her first, I knew she would be uptight, so I made it a flatter than normal approach. Turning final ATC has a SWA jet on the parallel runway immediately abeam us. She was so caught up in looking at that jet, she didn't feel the landing and was surprised when I powered up for the "Go" on the TNG. She no longer had a fear of flying and am glad I was able to get her to that point. Literally, she is 47 years old and only flown less than a half dozen times commercially. She taped her house when we flew over it as well as the attached landing into El Paso KELP RWY 26R.
Take your son, have him video or take pictures ... it'll be a blast. My son videoed and took pictures and was my first passenger post PPL.
Things NOT to do on first flight with new PAX:
1. No slips to land
2. No stalls or steep turns
3. Avoid high approach on final
4. Avoid Vx departure unless necessary
Basically keep it benign and boring.