Girls, look, I just noticed some redness on the back, it looks like…

Girls, look, I just noticed some redness on the back, it looks like allergies or hives? The baby is behaving as usual without any changes. He ate corn porridge with cookies, mashed carrots, and peach puree (peach was introduced for the first time, he used to eat apricot before). Or am I overthinking and it's just hives?