It was too late to do it last year, but I played around with one of those free Radio Shack barcode scanners last year with the intention of giving out coded ID's that could be scanned on entrace/exit to keep track of the kids' time. The downside is that you need a PC dedicated to this.
There are instructions on the web for hacking the CueCat to convert it to a keyboard wedge.
www.cexx.com/cuecat.htm When you scan the bar code it acts just like you typed it in on the keyboard. There is a free font available so you can create a report in your Access database to print labels with names and coded IDs. The hack just involves soldering a jumper to the PCB inside the cat.