Check this. Ask your son to log on, right click My Computer, select Manage. On the left, expand System Tools > Local Users and Groups > Users.
Highlight Users. On the right, right click your account, Properties. Check that Password never expires is ticked, and the other boxes are unticked. If any changes are needed, click OK. Then right click your account again and select Set password to reset your password. See if it makes any difference.
Check the other accounts as well (and apply appropriate password settings) and reset password.