When you get a jailbroken iPad, I'd recommend installing IncarcerApp - here's a review of it. It's a free tweak compatible with iOS 5 and iPad that lets you disable the home button and use an alternate volume-button-pressing method to access the homescreen. It also has extra features designed for parents helping a kid use an iPad successfully - rotation lock, alert blocking, etc.
You might actually consider getting an iPad 1, since it can be jailbroken on any iOS version due to jailbreakers having a bootrom exploit (very low-level exploit) available for it. The current jailbreak for iOS 5.1 on iPad 1 is only a tethered jaibreak, which means you need to boot the device by plugging it into a computer and running your jailbreaking tool, but that shouldn't be too much of a problem if you usually have a laptop nearby. Jailbreaking the iPad 2 depends on jailbreakers figuring out a totally new jailbreak for it each time a new iOS version is released, so if you have to restore the device, you might be waiting indefinitely for a new jailbreak to be released.
There are also special cases available for iPads that block usage of the home button - searching for "childproof iPad case" brings up a bunch of options.