4 y/o with bald spot on back of head. scalp seems normal no itching at all but getting bigger. causes? pediatrician or dermatology visit in order?

Bald spot: Many possible causes including simply being on his/her back too much. I would advise seeing the baby's pediatrician first, they should be able to determine the cause and generally you should be able to see your pediatrician a lot sooner than a dermatologist. Good luck

Derm consult: For evaluation of possible alopecia areata / need for biopsy. A dermatologist will need to see the child eventually. Best wishes.