My Child Started Out With What Looked Like A Small

My child started out with what looked like a small bite.. Well the "bite" turned into what looks like a bruise and has covered his arms and shoulders within 24 hours.. Took him to the ER stated it is not bruises nor is it a platelet issue. The marks almost look bruised then burnt. Not raised and not lesion.. Just marking.. Some spots seem to have a white dot in the middle while others do not.