SUPA105, this is a great idea, and it wouldn't matter if it was a two day course, one day course or half day course, so long as the participant came away from the weekend with some basic First Aid knowledge they would be far better off.
Personally, I wouldn't give a hoot if I didn't get a certificate, so long as I gained a little bit of current practice first aid knowledge I would be happy. Even if the instructor only touched on a particular section (eg. snake bite treatment) on the day, something which is relevant to camping, and this information was put across in an informal manner, and was also suitable for the kids to learn from. We all cart around first aid kits, perhaps even an inspection and suggestion session by the instructor would be a good thing.
My vote would be for a camping weekend, set aside a couple of hours in the morning, and perhaps a couple in the afternoon for the information sessions (I'll call it this rather than a course so we don't upset anyone), and all the family members can join in and maybe learn something.
I would rather attend this style of information session, rather than a regimented course.