With my grand total of no relevant experience or training, I think you must take the child directly to the hospital (assuming she'll survive the trip) rather than attempting experimental or half-remembered procedures that technically fall outside your remit and your expertise, in the back of the ambulance. As you say, the hospital is the place with the people who have the appropriate training, experience, equipment and facilities, not just in terms of treating the child, but also for looking after the parents. That twenty minutes later, the child was still not receiving treatment, is not your responsibility. It's a problem, certainly, but not a professional failing on your part - you had a reasonable expectation that the A&E staff at the hospital would jump right to it with all machines a-bing-ing and make a much better job of rehydrating the kid than you and your colleagues would have been able to.