Well, I am not an expert on tablets, but I work with some Intel ones.
Personally, I think it's much better to invest in a tablet than an e-reader. It might be even better to invest in a laptop. The tablet and laptop are like a desktop PC, they are general purpose computers. The e-reader is a special-purpose limited computer that will only read book files, usually, and not do anything else well.
The tablet is a bit more money, but if you get the right tablet, it can run all programs that a PC runs! Some tablets are like this, they are general computers, that will play any game, or run any application, and allow your son to expand his use of it. All laptops and desktops are like this, they will run any PC program.
This is very different from an e-reader, that I think won't do anything except read downloaded book files, right ? It cannot run any PC software, so it's not worth the money, unless it is very cheap ~ $100. It's basically an empty box with a picture of a screen on one side, LOL.
WiFi is an absolute must to have in a tablet, so it can talk to the internet through a wireless access point/ router. This is the box you normally have connected right to your cable TV modem box, and the other end of the modem connects your house to Comcast or some TV + cable service. Wireless routers are cheap, ~ 60$ .
WiFi: This way you don't need a network wire to talk to the internet and can surf the web on the tablet in your lap.
You have to have monthly charges, for cable internet service (like Comcast charges.) If you b uy your own cable modem instead of renting it from Comcast, you will save some money.
Also, with WiFi you can actually park at a MacDonald's, or sit in a Starbucks, or in a library, and use their free WiFi service, and through that, connect to the internet for free. And I'm sure most schools and dorms have this now.
I guess you also can get a tablet with a cell phone in it, and then you don't need a Comcast cable internet service. You can pay the cell phone company for a data plan, that will let you surf the web.
But note, I would not want a cell phone gadget near my body all day, turned on, due to the increased risk of cancer.
This radiation effect is not at all certain, so I would be cautious. Cell phone mfrs recommend you keep them 1 inch from your body. Or more. Just a note.
Another thing you may want, is a nice cheap B+W laser printer, for homework maybe. I have a Brother HL-22xx wireless printer, that is great, and cost me only $120 or so. You just stick a stack of laser paper in it, and it can print by a WiFi connection from the tablet. My exact printer number is obsolete, but they have new ones in this series. When the toner runs out, you can go to a Cartridge World (Fremont, CA, etc) and swap the toner cartridge for a refilled one very cheaply!
A laptop is also a good deal for a growing child, and is more powerful than a tablet for the same money probably.
But it doesn't have a touch screen, and is a little heavier. But Lenovo makes very light laptops, and they have frequent discounts.
Good luck ! I would get a tablet or laptop that can run most PC programs, and games, that your child will like. An e-reader is very limited. And these others can totally do the function of an e-reader with 1/10 of their brains.
BTW, a great game is MineCraft, that will run on a tablet or laptop. I think its cheaper ($24) on these PCs than it is on a game console. These portable PC's can take the place of a game console for many games...
Also, there is a lot of free software on say CNET.com that your child can use on these.
Good manufacturers of tablets and laptops are: Samsung, Asus, Intel (not sure if any released yet), Lenovo.
Lenovo is where I would always buy a laptop, they are very lightweight, and the company is great on service.