What causes a child to have Squint Eyes (Crossed Eye)?

I noticed one of my baby cousin has a Squint Eye. Though I was wondering what could cause this? Is it genetics? or what I heard is that, if you look at an infant from above as you lay them down, causing them to look upwards at you, it will cause them to have a Squint Eye as they grow up. Heck, I don't even know haha. Please share your knowledge about this. Thanks! ◕‿◕