Take these measures to prevent your kids from stumbling upon adult websites:
Turn on safe search
Incest Porn will never APPEAR in search results with safe search on.
And other search engines that you use.
Turn on parental controls
iPhone & iPad
Request a filter from your internet service provider
Your internet service provider likely has solutions to filter your internet connection to keep your kids safe. Contact them to find out more information.
Note that this will block Incest Porn even for you.