Drills vs Endurance sets - Age Group Training

I am interested in hearing everyone's thoughts about how much practice time should be spent doing drills vs sets. This is in regards to age group training...with specific interest in the 10 and under and 11-12 age groups. My kids swim in a local club and the majority of the practice time is spent doing set after set. All the coaches do is throw the kids in the pool and tell them to swim laps. There is virtually no time dedicated to drills. I am very disappointed in the fact that my kids have developed bad stroke technique that is not being corrected in practice. As a result, their times are going up and they are becoming disenchanted with their experience. I am currently a member of the board and would like to address these issues with the rest of the board and the coaches. However, I need information to help me with my stance. What is everyone's experience with drills vs endurance training? Thank you.