Phill,

As father of 2 little kids i do see them running around like little monkey's and it looks they are able to damage things where you never would thought about so my comment would be keep it as simple as possible with the less damage possibilty items on the boat. Even the adult people do have a problem to keep there daggerboards/rudder boards in perfect condition. The change of damage with this items is pretty big, so i would go for no daggerboards ( extra costs when damage ) and the simple as possible rudder system ( rope system ) and the possibilty to put them vertical up when on the beach , you know kids are just trying to sail the boat backwards on the beach up to the cantine to have a sodapop. If the rudders are horizontal behind the boats the change of damage is increasing a lot.
The mainsheet blocks also to be as simple as possible and open structured, you know also that the kids will drop it in the sand and don't have any idea what it does with the ball bearing. They only will say it is not running anymore and the parents have to try to fix it, this is also with the mast assembly, if it is going to be a 2 piece mast be aware that there will be sand between it and that kids just roll the sail up around the mast and put it in there sailbox, if the parents are not there to help them then they will not clean it with freshwater.
With other words it has to be monkey proof and with the lowest possible aftersales costs.

Regards,
Hans