Tympanostomy tubes (which help drain pus out of the ears to prevent chronic ear infections in young kids) are generally left in place between 6 and 18 months, after which time the child usually outgrows his tendency toward ear infections. It's unusual to have tubes for more than two or three years, since the eardrum usually pushes them out on its own before then. In fact, it's not uncommon to find them on your kid's pillow one morning, or for your pediatrician to see them in the ear canal during a checkup, and then take them out.
If your child's tubes haven't fallen out on their own (or your pediatrician doesn't see them in the ear canal), the doctor who placed them can remove them (a procedure that's done under general anesthesia, similarly to how they were inserted initially). Although if left in place for several years, ear tubes can puncture the ear drum, this sounds worse than it is. The small hole does not affect a child's hearing and usually closes on its own, though in rare cases, a minor surgical procedure may be required to close it.