In addition, it produces a distinctive rash on a child's arms, legs, and buttocks that looks like bruises ( purpura). Henoch-Schonlein purpura (HSP): This immune disorder can cause abdominal pain, bloody stools, and joint pain.It is usually triggered by a recent viral infection, where young children develop large bruises and petechiae (small purple dots under the skin) after an illness. Idiopathic thrombocytopenic purpura (ITP): In this autoimmune disorder, the body does not produce enough platelets.A low platelet count can be caused when platelets aren't being produced, are being destroyed, or are contained in an enlarged spleen. Thrombocytopenia: This is the medical name for a low count of platelets, which are important in helping blood to clot.It can cause easy bruising, frequent nosebleeds, heavy menstrual bleeding, and bleeding after surgery. Von Willebrand disease: This is a common and often mild genetic bleeding disorder.Likewise, bruises in specific shapes, like a large bite mark, cigarette burn, or belt mark can be signs of child abuse. Child abuse: Bruising on infants, unexplained bruises, and bruises in unusual places (upper arms, hands, ears, neck, buttocks, etc.) are considered suspicious.You would expect a larger bruise if your child falls out of a tree than if they trip on grass. Instead of simply looking at the size of a bruise, it is more important to think about whether or not the bruise is proportionate to the injury. Falls and injury: Not surprisingly, severe injuries can often lead to extensive bruising.