If you have no experience, this question will most likely be skipped from the start. Otherwise, tell the interviewer specific age groups. Do not say 'All age groups'. If you have worked with all age groups, break it down for the interviewer. Say I've worked with kids aged 9-11 at Camp Wakatooie in the summer of 2013. Then I worked with youth ages 5-13 at the local YMCA summer youth program, where we did so and so activities. If you only have had one experience working with youth, reinsure the interviewer that you can work with their age group by saying you enjoy being around all ages of children, and look forward to working with their group.