Allergic to mosquito bites?

i think my toddler may be allergic to mosquito bites. they become inflames and large. they also raise in the middle a bit and almost scab over. i dont know if its scabbing because hes itching them or not. i never see him scratching them though. the inflamed part gets pretty large and im worried that hes allergic to something, and wondering if its mosquitos. or does it sound like something else hes allergic to?