Inner ear problems are a cause for concern with children because they can lead to deafness. An audiologist can diagnose inner ear problems when your child's pediatrician has referred you to the audiologist. Here is how the audiologist "sees" into the inner ear, behind the ear drum, to find any worrisome situations.
A vibration meter has a probe that the audiologist inserts into the inner ear. The handheld machine itself sends vibrations into the ear, which reverberate through the inner ear and measure for reactions. If the auditory nerves and the inner ear anatomy react in the way the audiologist expects, it will show up on the meter. If the reaction is null or unusual, the audiologist will want to take a more in-depth "look."
An ultrasound machine made specifically for audiology can provide "pictures" of the inner ear. These pictures show the structures of the inner ear, the bones, the fluid behind the ear drum (if present), and the start of the auditory nerve. It is not a common practice, but one which the audiologist uses when other instruments do not seem to be revealing much about the potential problems your child is experiencing.
An MRI is only used in cases where there appears to be a definitive loss in hearing ability, and other measures cannot determine why. As you can imagine, it is difficult for children to spend time inside a large, noise tube of an MRI machine. That is why the MRI is only used to diagnose the most curious and worrisome of cases.
Additionally, the MRI can show abnormalities in the brain, problems with the auditory nerves and auditory nerve reception, and malformations or lack of the inner ear parts. If the MRI reveals any of these, then the audiologist can identify and diagnose the problem. Treatment may be possible following diagnosis, but only if the ears have something really minor wrong with them.
Surgery is an absolute last resort. That is because the inner ear structures lay behind the cheeks and sinuses of one's face. To fix something or see something via surgery, the audiologist would either have to go through the skull behind the ears, or through the passages in the face. The latter is obviously not preferential, which is why surgery is a last resort. If your audiologist suggests other means of finding out what is wrong, go with what he/she suggests. Consult an audiologist, like those represented at http://www.drmarkmontgomery.com, to learn more.