Assuming we're talking about non-jailbroken iPhones...
First, all apps on the App Store work
passively, meaning that the application has to be manually launched in order for it to send a location, or at least once since startup so that it's running in the background. If someone kills the task, the application will no longer track.
Alternatively, you can sign up for the AT&T FamilyMap for $10 per month for two users, or $15 per month for five users, and you can track any AT&T number, regardless if it's an iPhone or a dumbphone, and it even has scheduling and text messaging. It's available through their
FamilyMap website, and they even have an iPhone app.
As for remote wipe, it's only available for Exchange users and MobileMe users.
That being said, you can get a hosted Exchange account for about $8 per month per user (I recommend
SherWeb, as I've set up companies with them for over a year now and they work great with iPhones and Blackberries), but MobileMe can be cheaper, especially if you get the Family Pack, and it includes Find My iPhone.
Hope that helps.