unmet need for waterproof pumps and other medical equipment
I'm not sure of the reasons behind DUK not allowing kids with insulin pumps to attend camps, nor any children to bring mobile phones. Even during army basic training, soldiers are allowed access to their phones for a couple of hours each night. Although basic training is much longer than 1 week or 1 weekend, so perhaps it's more important to keep kids focused on what's going on around them, the people they're with and the activities they're doing.
Another potential reason could be the non waterproofness of phones and pumps. Actually, for phones there are loads of waterproof pouches, usually flexible, with roll-down velcro openings, sold by watersports suppliers, which are also ideal for blood glucose meters etc when canoeing, rafting, sailing etc - I used one for my meter when kayaking the Caledonian Canal for 5 days and several day tours, on multi-day sailing trips around British coasts etc.
I was made aware of the problems of non-waterproof vital equipment when volunteering with canoe club at a pool session for disabled children and siblings - one boy aged about 7 years had to leave the external part of his digital hearing aid on the side, which made communication more interesting - we had to swim in front of his kayak and attract his attention, so that he could lip read us. That works fine for canoeing, but must be much more difficult for swimming coaching.
Anyway, hope all volunteers and other participants have a great time on the trips - but don't rule out going on "normal" (ie not aimed at those with diabetes) adventure holidays. After several such trips, a lad aged about 18 years was a member of my "fire" (group) on an expedition to Greenland some years ago, and he achieved a first ascent of a previously unclimbed peak, skiing across glaciers, botany field work, built and slept in a snowhole etc, just like the other 11 young explorers - and caused my co-leader and I far less anxiety than another who sleep-walked (but couldn't open tent zips in his sleep, so it was only a problem when he slept in the snow hole, beside a crevassed glacier!) or another who moved rocks around with such enthusiasm that we were concerned about his impact on local ecosystems!