Brief is best
Coaching a youth swim program is a big responsibility. It requires a senses of balance, and the ability to keep a finger on the pulse of the group.
The primary goal of a coach should be to promote fitness, and safety in an atmosphere that encourages learning and positive self-esteem for all.
Some kids will be just beyond the "beginner" level, while others will handle everything you give them. The trick is juggling the group.
The abilities of each participant will be evident from the start, and a good coach will keep the group on task by inviting questions and offering answers that should help establish an environment of mutual respect by all participants. "Horseplay", "roughhousing", or "bullying" have no benefit to anyone. Safety is paramount.
The fundamentals of swimming should be stated and demonstrated so that each child can have a verbal and visual image of what you are asking. It is never to soon to offer stroke technique, but be sure to keep it brief and visual. Brief is vital in both instruction and workload.
Grinding out lap after lap will more than likely result in having a higher dropout number. Fun is the key to progress and retention.
Each practice should cover conditioning, stroke technique, and fun. 45 minutes to 1 hour is optimal time to establish this goal.
A favorite "practice" drill of age group swimmers is the "up-and-out". An "up-and-out" is sprinting across the width of the pool then pushing yourself up and out, diving back in and repeating 4, 6,or 8 widths. The emphasis is on upperbody strength training.
Another fun evolution is relay racing. It promotes a variety of opportunities for you as a coach to provide fun and instruction on various points: Starting, Finishing, and Patience on the starting blocks to mention a few.
As an age group coach you hold an awesome responsibility. Providing a safe and productive swim program can be a real challenge, by keeping it brief and fun will ensure your success.