Rash(?)

leigh

Hi guys! This is off topic. I have a little brother who's 9 months old and this morning he woke up with swollen rash-like on his arm, we thought at first it was a mosquito bite (because there was a mosquito inside his room that we saw this morning) but the rash was too big to be a mosquito bite and it's kind of worrying us. share any information you know. This is the picture: