Alopecia arita round circle me hair loss

There are a few very common causes of hair fall in toddlers and some are mild and easily treatable. But there are a few others that require treatment plans.
In your case, we won’t be able to predict anything. It is best advised to see a dermatologist. He is the best person, who can make it sure whether your baby is suffering from any skin ailment or Ringworm.
As you mentioned, your baby is having a round circle, which I doubt, could be Red circular lesions or round/oval scaly patches on the scalp. You may also be prescribed antifungal shampoos to cure the fungal infection.
Therefore, please see a dermatologist at the earliest possible.