I probably can't help you because the suggestions I have you probably can't use.
1) No blocking software can possibly keep up with what's out there.
2) Every parent is going to have a different opinion as to what is acceptable and what isn't. Also, their personal list will probably change with the age and maturity of their children.
3) By the time a child is old enough to chose to view objectionable material, s/he is certainly old enough to find a way around it. It isn't that difficult to do.
Suggestions:
1) Put the family computer in an area that is constantly accessible to all family members. No computers in their rooms.
2) Parents should make a conscious effort to monitor from time to time what is happening on the computer.
3) If a certain child's computer time has suddenly increased, find out why. Parents should know how much time is required on the computer to do the tasks their children need to do.
4) If you are using linux, it is relatively easy to have a separate user account for each child. Log all the internet history to a file controlled by root. The parent can then review from time to time the online activity of each child.
Parental responsibility is the only thing that works. The rest is something to sell to the suckers.
My opinion,
Fred