$15 for the 200MB plan is what I'd recommend. Data comes in handy not just for web browsing but also for GPS, e-mail, etc. If your kid wants directions to get back home, he won't be able to get them with no data connection (The GPS NEEDS a data connection to work).
If you jailbreak and get a pre-paid no data plan, this will work. Just make sure to change the settings to turn cellular data off.