no internet for other users?

I just got our home computer set up for internet last night and it works fine
when I'm logged in but it won't let my kids connect using their accounts.
It says the "user nameand/or password is invalid or expired"
I'm the computer adminsitrator and the kids have basic accounts (because my
**** has a habit of changing the settings if she has admin powers) I don't
want them to use my account when they are on line.
How can I fix this?
I'm not a total techID10t but some of this is too tech for me ...