So, clearly the AlphaSmart is fairly basic. The newer models are fancier, but as you can see from the web site, they are still limited, they run a proprietary OS that requires the purchase of additional software from the manufacturer, and they cost $400! Given the recent project to develop a $100 laptop for education, this seems excessive.
What does a young child need in a laptop? She needs durability (so no hard drive or thin lid with large display), reasonable battery life (so no hard drive), simplicity (so the OS needs to be hidden), a keyboard (no palmtops), and basic connectivity. It occurred to me that all of these things were features of my old Newton MessagePad 2100, except for the keyboard. But there was another machine using the Newton OS: the eMate. And the eMate fits this task perfectly, including the simplicity and power of an OS that is still unmatched today. This includes instant on, no need to explicitly save documents, the ability to install additional software, non-volatile memory (so there's no danger of you ever losing a file, unless you delete it), stylus and keyboard, etc., etc. Others have commented on using the eMate as a child's computer. You can get an eMate on eBay for less than $30, including shipping costs, which is a nice feature, too. The only question was: could I get it to work with today's computers?
Some of the eMates on sale on eBay will have power supplies and some won't. The one I bought didn't; a Radio Shack 3-7.5V, 2A digital camera power supply (catalog number 273-1696) works fine. Though nominally the eMate requires 7.5V (the original power supply was rated 7.5V, 1.2A), I found that the eMate complained about 7.5V but was happy with the power supply set to 7V.
Batteries are another matter. Odds are, the eMate you buy will have an original NiMH battery pack that doesn't hold much of a charge. You can either replace the cells in the batter pack or replace the battery pack with a holder for 4 AA batteries. As of this writing, I'm planning to do the latter.
The eMate has a built-in serial connector. I had a Keyspan USA-19Qi serial to USB adapter from an old Palm that I'm no longer using. However, the eMate's serial port uses a Apple mini DIN-8 connector, while the Keyspan uses a PC style DB9 connector. I had some Apple style and PC style cables and was able to make a DIN-8 to DB9 cable, given some information about the pinouts of the two ports. No doubt, I could have bought something somewhere, but I had the hardware and expertise to do it.
Mac OS X Software
Here you're in luck, as there is a (somewhat) active developer community out there for the Newton OS (which says something about the hardware's longevity). The software I chose is NewtSync, which aspires to be an iSync-like program for the Newton. It requires software on the eMate side, too, which can be installed using the NewTen package installer. With the TextSync plugin, my daughter can write papers using the eMate Notes program and then sync the notes to a Mac running OS X. Works like a charm. With other plugins, a Newton can be a perfectly usable PDA.