My dad's a little out of shape to play the game, but I've taken him twice and he's rented a mask and watched from the sidelines. He's slowly getting more and more excited about paintball and I think next time I take him he may pick up a marker with me lol.
But I think more important than having that time with your kid is seeing them happy. I can really tell that he's genuinely excited to see me passionate about something and enjoying it. Just imagine sharing that joy together...would be awesome. So I totally second your suggestion! It's a nice experience.