The skin bumps as you are describing may occur in a child for multiple reasons. Most common may be the skin infection due to staphylococcus aureus infection which causes Folliculitis or pyoderma. This condition is common during summer season. Simple daily bath with dettol and giving lot of liquids minimize this. Other condition can be allergic dermatitis which is dependent on environmental agents, dust, pollens, mosquito bites etc. The third cause can be small bleed into skin known as purpura. However, they are red initially followed by bluish discoloration and gradually changing to greenish, brown and disappearing- may be associated with bleeding from gums, nose and other mucosal sites. If you observe such type of lesions better consult your Pediatrician.