I am a bit stumped trying to get the parental control feature of profiles to work in any reasonable way.

I have set up our children to just watch up to M rating. Whenever you login to Lightbox it defaults to the main profile which is unrestricted. So it then requires manual parental intervention every time to change the profile using the PIN. This is far from ideal! Both the computer and the iPad app want to remember the main password to make it seamless to login to the site, and that is the way I would like it, but I was then expecting that you would be asked to choose a profile with a separate password for each profile so that you can just let the children get straight onto the correct profile.

Am I missing something here? The current system seems to require parental input every single time to make the profile system work, which sort of defeats the purpose somewhat...or is there an extra step I haven't seen?

In many ways I would prefer the way they implement ratings on a MySky - you just set a lower rating for everyone, and then you can override it with a PIN. Once again, can't see anything like this with Lightbox.