Welcome to HCM.
Thanks for your query
To compensate for the loss of blood by the fall, you can give him foods rich in iron (like green leafy vegetables) & Vitamin C
(like lemon, orange,etc.)
Other than give him a balanced diet rich in fruits, vegetables, fish, egg, milk, etc.
Also maintain adequate hydration & avoid junk foods.
Wishing your son a good health.
Thanks & take care