Vista - other user accounts unable to access internet w/ parental controls

As the administrator in Vista, internet access is fine. But, I have children
with their own user accounts set up who cannot view any webpages I've ALLOWED
using Parental Controls. REGARDLESS of the Parental Control permissions set,
NO internet access is allowed; once I turn OFF parental controls for other
users, the problem is gone and access is restored. But I still need a safe
web-browsing environment for them, though!

What is it with Vista, parental controls and IE 7 (which is the browser I
use)?