Two types of inflammatory and autoimmune diseases (excluding monogenic diseases) can be distinguished in children: those similar to adult diseases but with an early onset (type 1 diabetes, inflammatory diseases of the gastrointestinal tract, rheumatoid arthritis with anti-CCP antibodies) and those specific to children that are not described in adults (early-onset juvenile idiopathic arthritis with anti-nuclear and anterior uveitis). The familial and nosological aggregations suggest that these diseases are probably polygenically determined, and result from interactions with the environment. In a singular way, the incidence of adult diseases is increasing while the age of onset is getting earlier; conversely, there is no increase in early-onset juvenile idiopathic arthritis. On the other hand, the influence of early events that may alter the microbiotic environment is different for different diseases: whereas cesarean section (or early antibiotic therapy) has been shown to increase the risk of JIA and T1DM, it does not seem to change the risk of IBD. We hypothesize that environmental factors, particularly those related to diet and bacterial and fungal digestive microbiota - are different between these disease categories.