Need to know how to have my own iCloud account?
The only way to do this is for all of you to have your own iCloud accounts.  As long as you share the same iCloud account with your kids, or anyone, they'll be able to view and edit your documents.

You didn't mention the ages of your kids, but Apple allows you to create iCloud accounts for minors so you can have parental controls over various aspects of their accounts.  FWW, I had the same problem and created accounts for my kids and wife.  Doing that solved the problem for me.