The NIH periodically updates some of its most-referenced documents on pediatric prevention and care. This page is widely considered the gold standard in vetted and conservative recommendations for young athletes.
A quick glance at the page reveals its value: summary overviews of several injury types which are common to young people, including growth plate injuries, sprains, broken bones, and repetitive motion. Several of these are especially likely to strike three-season athletes or anyone focused on a single high-level sport to the exclusion of other activities.
The page also makes a clear distinction between minor bruises which can benefit from RICE therapy, and more serious injuries that require the intervention of a pediatric orthopedist such as myself:
Get professional treatment if any injury is severe. A severe injury means having an obvious fracture or dislocation of a joint, prolonged swelling, or prolonged or severe pain.
Kids know their own bodies best, but they aren’t always the best sources for candid information about pain. Try your best to open an honest dialogue about what hurts and how much, and you can prevent minor issues from blossoming into chronic conditions as your child enters adolescence and beyond.