Laying in prone (on the stomach) is a great position for preventing plagiocephaly, as the head is not resting on a flat surface. However, tummy time has a variety of great benefits. The child will develop more functional postural strength in the back and neck muscles, as well as increased head control. This can help prevent torticollis (read more).The movement of the head in the vertical plane also helps to develop a functional vestibular system for later childhood, and promotes healthy visual-motor development and depth perception.
As the child pushes down into the hands and shoulder girdle in prone, so as to interact with the environment, the child will develop more postural strength in the shoulders and form hand arches that are necessary for fine motor skills.
Tummy time is important for infants, but laying in a prone on propped elbows position (on belly with the forearms braced on the ground) is still beneficial for older children.