proteins
Proteins are found in every cell, your body breaks down proteins into amino acids and these amino acids are used to build and repair tissue. Children need around 1.2g to 2g of protein for every kilogram they weigh. They should get enough daily protein from their daily diet without needing to take protein supplements.
As guide, these foods contain 10g of protein:
50g of nuts
If there is not enough protein in an active childs diet, then they can become tired, and be slow to recover from injuries.