This is mainly an issue with young children between 1 and 8 years old who jam something up a nostril, such as a bean, pea, pebble or paper, according to eMedicine Health. Luckily, it's relatively easy to diagnose -- either the child will tell you what he did, or you may notice a discharge (often foul-smelling) from one nostril.
If you suspect your child has something in his nose, see if he can blow it out. If not, it's best to get him to the doctor immediately. Don't try to pull the object out yourself or push it down into his throat; that can do more harm than good. If it's nighttime when you notice the object, it might be OK to wait until morning to call your physician since most cases aren't life-threatening. However, if your child put a battery in his nose -- or food, which will swell in the nostril's moist environment -- call right away.
While most cases of foreign bodies occur in little kids, older children and adults can get objects lodged in their nasal cavities, too, if they fall or are struck in the face.