Your son has green fingers 😊.
@rarej also does and it's always a delight to see something growing from "nothing". I haven't tried being intentional with growing plants from seeds, but whenever I'm busy dicing (bell) peppers or tomatoes, I often throw the seeds in one of our empty pots and it's a roulette to see what sprouts out of it. One time, there were so many small pepper plants, that I gave them to my dad to plant in the ground.