I don't know the answer to your question, but if the kids are in any way IT savvy they will know that all they have to do is stick a pin in the reset hole to set the router back to default settings (including password). If they can't be bothered to set up the wireless element in order to get back on the internet all they then need is an ethernet cable or two...
If you are with BT (I don't know about other ISPs) you don't even need a login any more since you are identified by your line.