Android: I've often given my son my phone to play Angry Birds, and at least twice he's managed to delete contacts or emails. Android Parental Control helps users lock down their phones so kids can only use apps that you have approved; an admin password is required to access any restricted app.
The app can be set to launch as soon as the phone boots so clever kids can't get around the restrictions by rebooting the phone. You can also enable "Safe Sandbox" mode to show a screen with approved apps your kids can access. This is great for little explorers who are frustrated when they can't open the apps they want to try. The only apps they see are the ones you've previously selected that they can see.
The app works well and is free. If you want the ability to let kids play games or watch videos on your phone without having to worry about them accessing inappropriate apps or deleting info, you should definitely check it out. The app has not had an update since last December, but the developers seem to frequently use the app's Facebook page.
Android Parental Control is a free app available in the Android Market.
Android Parental Control [Android Market]