Why does my newborn have crossed eyes?

It takes them... ...Several months to figure out what they are seeing, and several more to figure out that both eyes are looking at the same thing; once that happens, they can adjust their vision so that the information from both eyes is fed to the vision center of the brain to make one 3d picture of the surrounding world.
Not unusual. Many new borns need time to align their eyes. In the newborn nursery, there is a very large percentage of children with their eyes turned in. Only 2% have their eyes turned out. If this misalignment is not resolved in the course of the first month, certainly a visit to the pediatric ophthalmologist may be necessary.
A new born baby. Has a visiualize system that will develop with time. Typically new born babies eyes wander until about age 3-4month.S when they can start to focus on things. If your new born baby has eyes that are not only wandering but turning in a noticable amount it is best to see a pediatric ophthalmologist , your baby may have congenital estropia.
It could be normal. Newborns can take up to 3 month to start focusing, so a bit of wandering of the eyes is normal. That said, a frank deviation could mean that the baby is not seeing as well out of one or both eyes. I would ask the pediatrician for advice.
Should improve soon. New babies often have disconjugate gaze (the eyes don't look in the same direction), especially if they are not trying to look at anything. The gaze should straighten out over the first 3 months, but parents should let the doctor know at the 2-week, 1-month, & 2-month check-ups about the gaze. Babies with disconjugate gaze after 3 months, or who have additional symptoms, should see an eye doctor.
Normal. If it is intermittent it is common for fist few months if life when the eyes are just starting to be able to focus. If constant or persistent after 2 to 3 months notify your pediatrician.
Eso. Your newborn may have strabismus, or misaligned eyes-- it is important to determine if the baby has true esotropia or pseudo-esotropia. Make an appointment with your nearest pediatric ophthalmologist for an evaluation.
Normal for age. Infants have an immature nervous system and can have intermittent eye crossing during the first few months of life. As they age this matures and between 2-4 months of life you should no longer be seeing any eye crossing. If the eye crossing is still seen after 4 months, or if it's persistent in the first 4 months, let your pediatrician know immediately.
Very common. Newborns and infants can often have crossed eyes periodically especially when they are tired or trying to focus on an object. The eye muscles are somewhat weaker this early and don't always work together. If the crossing is frequent or remains then a pediatric ophthalmologist should be consulted.