Keratosis pilaris is commonly called "chicken skin," but I found this from an RD:
Kids often eat too much processed foods and not enough nuts, seeds, olive oil, or other basic essential fats. Poor fat consumption can cause a wide variety of symptoms, including “chicken skin,” Dorfman says. Unfortunately, this condition is often misdiagnosed as keratosis pilaris, a skin condition in which red bumps appear on the upper arms, thighs, and cheeks.
If patients have bumpy skin and their diet reflects a lack of essential fatty acids, suggest they change their diet to include essential fats found in foods such as walnuts or olive or flaxseed oils and take fish oil capsules, a quick fix that provides the proper fats and will clear up this type of rash.