How do you become cross eyed?

Different reasons: While most cases of crossed eyes are inborn, there are a few that may be acquired after birth. Paralysis of one of the eye muscle nerves may cause this. That can be caused by different disease, including stroke, tumors, demyelinating illnesses etc.

Varied: You probably mean: congenital esotropia, accommodative esotropia from hyeropia in kids, other: sensory exotropia from blind eye, cranial nerve palsy, thyroid eye disease.