"Net Nanny for iOS is a fully-featured Internet browser for your smartphone or tablet. Other browsers, Safari, must be disabled in the setup process.
NET NANNY FOR IOS includes Filtering (18 categories), Age-based Profiles, Safe Search, Profanity Masking, and supports Wi-Fi/3G/4G.
NET NANNY SUITE FOR IOS includes all the features of Net Nanny for iOS plus Remote Administration, Reports, Custom Categories, Whitelist/Blacklist. Future releases within the next few months will include Time Controls, Custom Alerts, Reports, and device management tools such as Device Locate and Forced Ring. All new features will be auto-updated for existing users."
I think K9 Web Protection would be worth trying, especially since it's free to try. It doesn't have all the features of WebWatcher, but it has one thing that you need - it works on iOS. Here is a side by side comparison of the two.