I'd go with a low pro for sure. If you're looking for a good starter reel, check out the Abu Garcia "Black Max".
http://www.abugarcia.com/abugarcia-reels-baitcast-reels-low-profile/abu-garcia-black-max-low-profile/1373565.html
I agree on the Black Max low profile but not so sure if a 7 year old is ready for this style of reel. I have a couple of these reels and they perform good for the money.
Really take the time to setup the reels for the rod, the target fish species and water conditions which will lessen the inevitable birds nests. I spent quite a bit of time in the local school yard after hours practicing 1000's of casts with just a small bell weight tied to the end of the line to really get a sense of the reel different rod lengths, the braking system and my own initial limitations with using this style of levelwind.
To save on the aforementioned birds nests, find the max cast distance that your son can do then take a piece of electrical tape and place on the line in the reel. That way, when he gets too zealous or careless in his casts (and he will), the tape will stop a birds nest from forming deeper into the spooled line on the reel. To help untangle birds nests, I invested in a cheap ($10.00) dental pick set from Amazon which works amazingly well to get into the tight confines of the reel to sort through the tangles.
You will also need to spend time with your son in using the reel and rod in wind conditions. I have found that levelwind reels and wind do not always play nice together and also depending on the wind direction. I will switch to a spinning reel if the wind starts to pick up past a few miles per hour.
I find that with these reels, in the right hands will outcast any spinning reel in terms of distance, smoothness and not to mention - no line twist.
Typically for river shore fishing such as the upper Thompson near Kamloops, I use the Black Max with braided line on a medium light 8 or 9 foot casting rod. For lake fishing (trolling) in a boat, the levelwind is superior to a spinning reel and I typically use a 6 or 7 foot lightweight rod as it easier to work with (lengthwise) in my tinny.