There is probably not a subspeciality where you could avoid infants or toddlers in pediatrics, outside of maybe pediatric psychiatry. But I would agree that pediatric rheumatology probably has the lowest population of infants and toddlers. I mean, you still would have to deal with potential consequences of maybe vertical autoantibody transmission and maybe the rare congenital HLH, but otherwise, autoimmune diseases are very rare under toddler age because you need an robust immune system and the potential trigger.
I mean, if its an organ that you are born with in a fully developed state (ie, every organ except the immune system), you can have it be abnormal from the get go and have to see patients in their infancy.