Great kit. I'm loathe to suggest additions because of the weight, but a few thoughts from some limited scout experience -

1. A few spare plastic bags - just for carrying / bundling wet kit
2. Esbit stove or similar, and instant hot chocolate - easiest way to get a kid who has fallen in water warm and feeling OK again. Plus in wet woods esbit tabs are a great way to get a fire started
3. Does the fak have OTC meds for small kids e.g. liquid NSAIDs? Calpol (or whatever ibuprofen solution is called in US) sachets can be a godsend
4. Bag of hard candy - always useful as a bribe / reward / morale booster

Do the kids carry anything - as per the excellent post put up recently? Just a garbage bag each would save you carrying and if the group got stranded gives everyone shelter