Generally, younger children are more prone to infection because their Eustachian tubes are more narrow and their immune system are less mature.
Ear infections usually first develop around 4 to 6 months old, after a baby’s first cold or other upper-respiratory infection, which causes buildup and inflammation in the Eustachian tube. Two or three ear infections a year are generally not cause for concern, as long as the fluid clears from the child’s ears between infections. A pediatrician will be able to detect this at follow-up visits.
Although some temporary hearing loss almost always accompanies fluid in the ear --with or without infection--the fluid can become so thick that it interferes with a child’s ability to hear conversation. Monitor your child and if this persists for months at a time, especially during the first year, when he’s starting to process language. It can result in delayed speech. Signs of normal hearing include being awakened or stirring at loud sounds, being calmed by familiar voices, noticing rattles and other sound-making toys, crying differently for different needs, and responding to the change in tone in your voice.
It’s not until age 4 or so that most kids outgrow ear infections, when the eustachian tube lengthens, widens, and becomes more vertical, making it harder for bacteria-laden fluid to back up.