I just recently installed Elementary in Virtualbox without an issue. Can you share a bit more information?
Where in the process are you getting stuck?
If you use the Wizard to create the machine, you may have to go in and designate the ISO to run after the machine has been made.
You can go into settings, and select your ISO the first time you attempt ...
I have the same issue. The parental control does not do anything.
My current workaround is to use ufw. For my son, I wanted him to only be able to get and send email on his own, hence I allowed only outgoing connections to the smtp (587) and imap (993) ports of his email account, as well as to dns (port 53):
sudo ufw default deny outgoing
sudo ufw default ...