The first one is allergic purpura. The red dots of allergic purpura appear symmetrically on the extensor side of both lower extremities and can be accompanied by petechiae, joint pain or stomach pain. The second, immune thrombocytopenia, can appear pinpoint red dots on both lower extremities, and when you press the red dots with your finger, the red dots do not fade, this time you can take your child to a routine blood test to see the number of platelets.