Children can be born with squint or develop it in childhood.
It can be constant or intermittent, occurring when the child is tired or daydreaming. It can also be alternating, sometimes seen on the right and sometimes on the left eye.
When the eyes are straight, images formed in each eye are sent to the brain and it is fused into a single, three dimensional (3D) image which gives us depth perception. When a child has a squint, two different images are sent to the brain. The brain learns to ignore the image seen by the misaligned eye and after some time the image is being suppressed.
This condition is called amblyopia or lazy eye. Adults who are recently diagnosed with a strabismus often complain of double vision (diplopia) because the brain is unable to ignore the different images.