Children in the Learn to Train stage of development should be practicing predictable meal times and routines including breakfast as the most important meal of the day. These practices should have been established during the FUNdamentals stage of development but it is never too late to start good habits and these practices can always be introduced, improved upon, or modified as needed.
This process should be led by parents or caregivers with the support of coaches, teachers, and others with an influence on children's behaviour.
It is worth noting that quality nutrition and good meal routines reinforce the circadian rhythm and good sleep routines.
The following links point to resources that have been collected and are relevant to this skill (?).
Sleep, Recovery, and Human Performance, is a 20 page pdf document put together by researchers in Calgary for Sport for Life. It discusses the importance of sleep and recovery for sport performance and some of the most prominent sleep disorders and factors that affect one's sleep and recovery. The document is very clearly and consisely written to discuss the key factors across all LTAD stages.