you'll have to login into the user's account and change network settings, which requires administrator password to make changes. go to control panel, then network sharing center, then change adapter settings, then right-click on local area connection, then select internet protocol version 4, then click properties, then select use the following dns server addresses, then enter opendns adresses into the fields, then click ok and close. at some point during this you'll be prompted for admin password. that's it.
be sure that the user is a standard user with parental controls and not an administrator.
note: user may still be able to go to google image search, turn off google's search filter, do a search for porn and view porn related images which will include all kinds of porn. therefore, parental supervision is still required.