Children usually consume what they have been given and sometimes either overdo it or even don’t eat or drink at all when excited.
Parents need to encourage their children to drink during long training sessions or the kids can become very cold and shivery. A 1% decrease in body weight already has a detrimental effect, e.g. dizziness, light-headed, loss of balance. It is also very important that your child drinks plenty of fluid within the hour prior to the training session. Sports drinks containing carbohydrate, protein and electrolytes are recommended but should only be complementing lots of plain water and not be the only drink available.
Children should ideally eat 3 hours prior to the training session a filling meal with plenty of carbohydrates and energy giving foods. That is however not always possible and so food should be given as early as possible prior to training if the young person can tolerate it.
Some kids can eat directly before swimming whilst others can’t. It is never recommended that a full dinner is eating within a hour of training but lighter foods should be given instead.
After each longer training session, energy reserves need to be restocked immediately and it is highly recommended that kids need a milky or fruity drink e.g. fruit juice, smoothie, milk shake. Also a snack must be provided within half hour of stopping training. Best suited is bake ware, sandwiches, fruit to be followed by a cooked meal when home.
Sporting children need 500 – 1000 calories more per day than non sporting ones. That would make around 2200 calories for a 12-year old. However please check and see whether your child is actively overweight or underweight and adjust accordingly, if in doubt, seek doctor’s advice.
Giving Nutrition Advice to Child Athletes — Active Kids Have Special Requirements for Top Performance
Nutrition Numbers for Active Kids and Teens
Protein aids muscle recovery when consumed after exercise and should account for 10% to 15% of calories. Recommendations for total protein intakes are 0.95 g/kg/day for kids aged 4 to 13 and 0.85 g/kg/day for adolescents aged 14 to 18.
Carbohydrate is the most important source of energy for an active child or adolescent and should represent 55% of calories (more on heavy training days), about 5 to 8 g/kg of body weight.
Fat should account for 25% to 30% of total calories. High-fat foods may cause discomfort if eaten too close to the start of physical activity, but some fat is needed on a regular basis for growth. Emphasize healthful fat that’s found in avocados, tuna, canola oil, soy, and nuts.
Fluid intake should be supervised and monitored during and after physical activity. This should result in an hourly fluid intake of 13 mL/kg (6 mL/lb). Fluid replacement postexercise should include about 4 mL/kg (2 mL/lb) for each hour of activity. More is needed for kids who sweat heavily.
Sporting children should consume more smaller meals throughout the day, rather than 1 large one. Sporting children generally eat more calories than their parents. So parents beware, as if you eat as much as a swimming youngster, but are not sporty yourself, you’ll put on weight.
Source: Today’s Dietician and part own experience
A great source of information is also the Performace Meal Wheel,
I personally do not recommend that children be given supplements that are generally only suitable from the age of 16.
See this very important article about Protein supplements