Sorry for the duress your child's hair issue is causing you. Perfectly understandable.
Still not 100% certain it is childrens AA. So until we can make a more definitive diagnosis, I did a quick google to confirm some symptoms of Alopecia areata and this is what I found that might at least might offer some insight (hopefully):
To date I have not found itching/inflammation associated with A.A.? Do you notice any evidence of flaking or scaling in child's affected region (crown)?
According to a couple sources inflammation or scaling is not present.
Approximately 25% of patients show grid like pitting in their nails.
It's origins are still unknown, yet it is not considered contagious.
@20% of patients have at least one family member with a history of A.A.
80% of children make a complete recovery(1 yr.) New hair's pigment can initially return lighter/white color.
This typically resolves itself and original color is restored.
I hope you'll soon get this satisfactorily addressed so you can aim your focus at your beloved son's complete recovery.
Whether or not this applies to your child's symptoms this image may give you a little better idea what nail pitting can look like?
All my best.