My young teenagers volunteer every summer as Water Safety Instructor (WSI) Aides for College Stations Parks and Rec. Children have to be 12 yrs old by April 1. There is a (free) 2-week WSI Aide class during the first session of swim lessons (first 2 weeks of summer vacation). They then assist the WSIs during swim lessons. At 16 yrs, they can be a WSI and get a paycheck.
At 15 yrs, they can also take American Red Cross Lifeguard Training. There's several local pools that will be hiring for the summer.