are you happy that this is the way to handle your obvious concern? I'm the first person to agree that the Internet can be a dark and dangerous place for the unwary, and as a parent myself I wholeheartedly support your admirable desire to protect your children from harm.
My experience however, is that if they suspect subterfuge children can react by becoming secretive, and that's the last thing you want. You don't mention the ages of your children, but perhaps a chat about why you feel worried might help a lot. Children like the feeling that they are being protected by parents, but they have a natural and healthy desire for independence, and if they are at all computer literate they'll soon find a way to beat your system anyway.
Please forgive me if I sound at all intrusive - it's for you to decide how to raise your children - but I have some experience of advising a large national institution on how to protect the children of their employees when they go online. So many people with children work at this establishment that they have an onsite school for juniors, and I advised them on this very subject. They have found that talking frankly to the kids about the dangers, and why they (teachers and parents) might seem overly protective, has been well-received by the children.
It's horses for courses though, and you are obviously the best judge of what's right in your circumstances.