It's an opportunity worth capturing while you have the chance, and at age 7 anything in a 4wt to 6wt range will do as long as the experience is memorable. I took my son for bream (sunfish) at first. My daughter also enjoyed it (once)
Use a small de-barbed fly, preferably a small popper. I prefer a location with comfortable shore access, like a beach during the offhours where the casting is easy and the fish are visible.
The commotion may attract a bass or pike, which introduces the concept of big game into it, something to exploit at a later date. You won't hook one with the popper (most likely) but the predator may come in and chase the bream around which leaves an impression.
I wouldn't worry too much about the brand name or long term durability. Important thing is that it feels comfortable (4-5wt no more than 6wt) and that you take him to an easy, safe and interesting spot.