This isn't the latest Android device, but it's only around $50 and does most of the same things the iPad will do. It runs the Android OS version 2.2. The current version of the Android OS is 4.0. This is also a refurbished model but definitely very capable with a Dual Core Processor and 2GB of built-in storage.
This model comes with the latest Android OS (4.0) and has 8GB of Storage for around $250, Clicking Buy Now just takes you to the specifics page;
Modern LED LCD screens, HD TVs and touchscreens use HDMI cables to send the video and audio signal. Cables in lengths of 6ft are sufficient for desktop scenarios but where the CPU is further away from the actual screen, as in home audio situations, cables of 20ft are a good size for typical rooms. These are AmazonBasic branded cables, some of the first products I've seen to actually carry the Amazon sticker as a store brand, and seem to be the most cost effective for the features, including new draft standards. About 3-4 of the shorter cables on hand would be adequate and 5 or more of the longer cables;
Samsung and Dell both make some decent "smaller" sized printers that are compact and can be very portable if needed. These are black only, please let me know if color is necessary as it will add more expense to a laser printer. For quick, cheap blank only print outs this is the way to go. HP is the highest priced, listed last and not as portable/compact, but HP has always made some of the most reliable printers.
Several tablets on the market today are comparable in features to the Apple iPad, but are significantly lower in price. The Nexus Tablet and Samsung Galaxy Tablet are great alternatives. Both brands have the full capability of wireless broadband internet and both have a Wifi only version (if you already have wifi at home and plan to use it mostly at home, 4G is not necessary, but not a significant additional cost).
Ordering a MacBook Pro from MacMall offers a little bit of a discount over buying directly from Apple. They buy in bulk so can offer a quantity discount. Apple likes to fix prices across vendors now so it's hard to find anything less than what the Apple Store itself has. MacMall can also offer some promotional deals from third parties such as a free printer sometimes if that's something you're interested in. (Clicking on "buy" below just takes you to the page where you can compare or order it). The current promotions offer a "free" update to the latest Mountain Lion OS, OS X 10.8. Also with a mail in rebate you can get Parallels Desktop 8 for "free", at $49.99 and a full mail-in rebate (select uninstalled, rather than installed, they'll just send the CD). Parallels Desktop 8 lets you run Windows right on top of your current OS X if you need it. More information here;
In regards to a solution to keeping children safe online, and limiting web time. One quick solution at the network level may be to look at some newer routers. For less than about $80 there's a couple at Wal-Mart that have a lot of these features. Above is the price on Amazon you might compare if you take a look at the models they have on the shelf.
Here's is the overview/specifics sheet in PDF of the Norton Parental Control software that comes on the router;
I would also certainly sign up for this service below from Norton and try it out first, it is free to use, while the router filtering service on the router above "protects" your kids from inappropriate sites, it didn't appear to have the time of day functions like this Norton Online Family does, which would allow more of the dedicated daily study time (no internet between 7PM an 9PM for example); both will give you reports for an additional fee, but this may be all you need right now;
Be sure to watch the video on this page on the bottom right for an overview.
I believe it was on TV some evening this week and I only saw the end of it, all of it now, but it gives some insight into the trends we're seeing with students and technology lately, both positive and negative.