Thanks for the replies guys -
It was in an inlet, and yes, there was a tide we were against too.
I chose the location for it's safe location, as it is fairly sheltered and quite shallow - almost ruined my newly made daggerboard!! Well, took the paint off parts of it - oh well, I'll probably fix it up after the Summer.
From a safety point, we all wore PFA's, with whistles and had a paddle, despite the water probably not much above waist deep for the most part, but I appreciate your concern.
I ended up just pulling the boat back after 3 hours of 'messing about'. That took all of 30 mins - shows how little progress we made!
Both kids are excellent swimmers. In fact, I'm proud to say that my youngest (11) saved a classmates life this year during a pool field trip - actually saw him on the bottom of the deep end with bubbles coming out of his mouth and dove down, brought him to the surface where lifeguards got him breathing again!
Back to the sailing - after reading the replies, I'm convinced the weight was the problem. I should have thrown one of 'em overboard I guess!
One more question... If you try to sail within 45 degrees of wind, what happens? Maybe I was trying to sail at 40 degrees!