When your child is stuffed up with a common cold, most of the mucus drains from the nose into the throat. The mucus that does not drain gets backed up behind what’s called the tympanic membrane or eardrum, which is a little window that opens into the middle ear. The eustachian tubes are responsible for draining the fluid that ends up in this tricky spot into the throat, but that’s not always what happens. Because kids’ immune systems and ears are immature, they become more susceptible to infections. The main reason little ones are afflicted with ear troubles is due to anatomy. Their eustachian tubes are shorter than in a full-grown adult, and they tend to be oriented more horizontally, so it’s harder for fluid to drain out. Pre-existing bacteria make their way into that fluid and breed.