I have taken lots on little kids sailing before, in lots of different boats. The other day i took 4 children sailing, for some it was there first time.
The kids ages ranged from 6-13.
I took them out in a topper, I found this boat very good for having lots of people on (We had 5 on at once) And it was also suitable for letting the kids have a go at helming while being close enough to take control if need be.

So for those people who want to get there kids to have a go at sailing toppers would be one for the boats I would recommend as a very good play boat.

here is a video to show you what its like...

At the end there is a bit showing just how many people can get in while still sailing well!