My DS has a similar things probably 3 or 4 times from when he was about 9 months to nearly 13 months. It would come up mainly on his legs and arms and sometimes on his face and hands too. They were very red and slightly raised and kind of looked like mosquito bites that had been scratched. I took him to the Dr and he said it was hives and was a reaction to a virus to which he had come in contact with. They did not appear to be itchy and didn't bother him and would just come up and then just as suddenly dissapear. Maybe get a Dr to check it?