A child is only as energetic and enthusiastic as it feels fit. As far as nourishment can help there are a few essentials a parent has to know.
Please refer to my Nutrition page for further tips or look up the basic information links below:
The NHS publishes calorie guidelines for children and teens, but, a child that swims more than 1 hour sessions, requires more calories than others. I add more calories to the daily intake if swimming sessions exceed 2 hours per day and sometimes we train twice per day.
The Canadian Paediatric Association publishes tables for sports active youngsters.
As a general rule, your swimmer is most likely to need more food than the parent.
It is not necessary to give your swimmer energy bars, normal food will do.
Though nowadays on poolside, during competitions, organisers do not allow food but energy gels are permitted. I suppose it makes sense to avoid food waste getting into the pool.