Why do some children have misaligned eyes?

The condition where the eyes are misaligned is called strabismus.  Different types of this condition exist.  The most common among children is esotropia (inward deviation of one or both eyes).  The less common type is called exotropia (outward deviation of one or both eyes).  The rarest is a vertical misalignment wherein the one of the eyes is deviated upward (hypertropia) or downward (hypotropia).  The deviation may be present intermittently or constantly.  Treatment options depend upon the type of deviation and may include glasses, prism, and or surgery