Children between six months and four years of age are the most susceptible. How they occur A middle-ear infection occurs when bacteria or viruses invade the middle ear, a small space behind the eardrum. This usually happens following a cold. That's when fluid builds up and an ear infection can develop. Bacteria grows in the fluid.
Pressure then builds, causing pain in the middle ear.
Colds , sinus infections, allergies , and nasal congestion can all contribute to middle-ear infections. If your little one is in day care, be prepared for frequent colds and ear infections. The more children your child is around, the greater the risk of exposure to bacteria and viruses. Symptoms Toddlers as young as three can tell you when their ears hurt. But infants can't explain how they feel.