I would also observe the coach working with a group of players or even a private lesson to see what his or her style is like. They have extensive knowledge from a technical standpoint. They have an understanding of the mechanics of the sport. They also have knowledge in the areas of marketing, management, and things like that, in terms of running a club and not just specifically teaching tennis. They must have organizational skills, and they also have a lot of contacts in the field in terms of developing programs for player, league, social events, etc.
Children are very prone to fall when playing tennis.
Balancing with a racquet in your hand, and balancing on one leg and going through the ground stroke motion. Technically water is the best drink to have while you're actively playing, because it's easily absorbed into the body system. The sports drinks are high in carbohydrates, which gives the players more energy, particularly during long matches or in the hot summer heat. Make sure that their stomach does not get upset. If a player wants to use a sports drink while playing, I don't discourage it, but I often recommend that they water it down.