If your kids really never use the net unsupervised, then, parental control is not really needed.
The white list approach is extremely cumbersome, and often fails to work as you have discovered. You may need to add 10's of sub-domains to be able to access several sites properly. It can also prevent you from login in to many web sites as they commonly use some special login domain. It also can prevent captchas from working.
OpenDNS is a viable solution as it rely on a grey list/black list model.
The black list actively block known malicious sites, and the grey list apply to the inappropriate sites, like adult content.
It is set up so that sub-domains do pass correctly.
A great advantage is that you don't have to hunt for appropriate sites as there is a crew of very competent peoples who constantly do it for you.