a couple thoughts-
90% of bearded dragons are super mellow and easily handled. I gave my son his first pair when he was 6 and he was actually able to care for it himself, with only minor parental supervision- mainly in the form of reminders to clean the paper and water bowl from time to time. My son is now 11. His dragons have spent countless hours lounging on him while reading or playing video games. He has a doll bed that he tucks them into to sleep every night and every morning he puts them back in their converted south-facing bay window with a plexi wall they can't climb over where they spend the day while he is at school. He can give them treats of human foods, he bathes them, finds them edible weeds and bugs in the warm months, and he gets a break from animal ownership for a few months each winter when they hibernate (they like to do that on the cool hardwood floor under the TV stand) and they breed and produce wonderful babies each year. They even go on some outings with us when the weather is appropriate.
They are real "pets".
Chameleons- really for a 6 year old, this will be your pet and the 6 year old can admire and join in a little. It involves lots of insects - more than most 6 year olds can deal with (bearded adults- insects are only a very small part of a well rounded diet- my son only feeds his occasional insects he catches during the summer as treats, the bulk of the diet are rep-cal bearded dragon pellets and fresh leafy greens).
As far as handling- chameleons really aren't that much "fun" to handle. Most 6 year olds will not like an adult chameleon crawling on them for very long. It looks like a lot of fun, but they've got pointy claws that they dig in when they grasp what they are climbing on. Panthers are a bit better than veileds, but still most 6 year olds probably will be very uncomfortable in the pointy grip of a chameleon. Veileds especially have a very strong grip and leave track marks even on a grown man.
Chameleons are more like tropical fish- beautiful to look at, fun to keep in a nice terrarium with foliage, fun to feed, but not so much fun to handle. The chameleons don't like handling so much either.
If he wants a "pet" that can be held and interacted with and a pet that he can have more of the responsibility for caring for- reconsider a bearded dragon and go meet a few more. If you found an aggressive one, then you found the 1 in 50 or so that is the exception to the rule. Most are extremely mellow...
Edit- I've bred both by the way for many years. My son's experience is not exceptional, except maybe his interest in lizards is a little more than most boys. But temperment wise- bearded dragons way to go- very easy. I can send you a care guide if you PM me your e-mail address. Chameleons are way more complicated and fragile and hands offish.
