Lion Installation Problem-help!

Yesterday I installed OS x Lion over Snow Leopard. Everything seemed to go very smoothly until I rebooted; at the login screen there is only one user, one of my grandchildren who, because of her age I have parental restrictions set up.

I am now in the situation of no access to my data, can't load progams like terminal etc. Is there a way to at least get to my data or better still a way of adding an administrator account. I do have an old backup of Snow Leopard, but I don't want to go that way if there are other solutions.

Your help will be gratefully received.