Help with Public Computers

[Michelle]

Hi, I work at a small museum that has four public computers for kids.
We do not typically get high volumes of children to use these
computers but noticed one day after a particularly rowdy group that
some of our computers were "tampered" with, meaning the kids had
accessed the C: drive and were playing/deleting some of the files
within. I was wondering if there is a way to disable the start button
on these computers but still be able to access it as the
administrator. Would I have to create an administrator/User account
seperate from the Guest account and if I disabled the start button
would it effect both accounts. I was also wondering if I could limit
access to the internet or put some parental controls on the accounts.
I really just want the kids to only play with the games we have on the
computers for them and some pre-approved websites. Thanks!