Children in the Learn to Train stage should limit and control "screen time" in the evening prior to bedtime and maintain a 15-30 minute regular bedtime routine. Children should also get early morning light exposure every day.
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.