For about the first four months of life, babies think that when something is out of view, it’s gone for good. That blanket or pacifier that drops to the ground is gone forever. At around five months, however, babies learn that their favorite toys,…

For about the first four months of life, babies think that when something is out of view, it’s gone for good. That blanket or pacifier that drops to the ground is gone forever. At around five months, however, babies learn that their favorite toys,…