How do you keep your energy level and stamina at a high level? How many children have you cared for as a group at one time?
Some interviewers like to put people on the spot with questions like these, but don't fall into the trap of conceding that you have weak areas that could knock you out of contention. Address how your energy level and stamina meet the requirements of the job and give hard evidence if at all possible in the form of references and documentation that includes facts and figures. It's an opening for you to describe not just what you do but how well you perform childcare. Taking the interviewer through one or more of your memorable childcare events for instance is often a good approach. Your response should be enthusiastic, confident and heartfelt.