Movement is a baby's first way of communicating and producing social interaction. In many cases this is accomplished by using their motor skills to look at, point at, move towards, or go get an object of interest.  A baby can use several motor skills through non-verbal forms of communication to begin developing their early language and social skills.  These motor skills include:

Head control/gaze stabilization: in order to look at objects of interest and interact with people in the environment socially, a child first needs to develop adequate head control.  This includes holding their head in midline when sitting with support or on their own and maintaining their balance in these positions during neck movements like turning their head right and left in order to look around their environment.

Trunk control and arm use: in order to begin pointing and interacting with objects of interest that can be used to shape non-verbal communication or a social interaction, a baby needs to be able to stabilize their trunk in a desired position, such as sitting or supine, while using their arms to engage.  Their trunk stability needs to be adequate to reach outside their base of support and use both hands to manipulate a toy in their desired position.

Movement through space: whether this is crawling or walking, a child's ability to move through their environment opens up several doors for a child to communicate or interact socially.  For example, now they can move towards the object they'd like to communicate about.  They can go get these items and bring them back to the person they'd like to socialize with in order to facilitate that social interaction themselves. For many babies, movement through their environment is their first opportunity to initiate social interactions.  It is during these early motor skills that kids learn language skills like:

Joint attention: This is the ability to coordinate their attention between a family member or caregiver and another object.  They do this by looking, pointing, or moving towards a toy and then looking, gesturing, or vocalizing back to the person they are socially interacting with. A delay in demonstrating joint attention through motor tasks is one of the early warning signs that a language delay may follow.

Reciprocating babbling: This is the baby's ability to repeat back vowel or consonant vowel sounds. For many babies, communication with parents and caregivers changes dramatically once they are able to reciprocate back these vowel and consonant vowel sounds.  They achieve the ability to participate in reciprocating babbling by attaining an upright posture through sitting skills that allow for the increased expansion of the rib cage, increased respiration, and increased ability to produce phonation. Once producing sounds through reciprocating babbling a baby further learns to control the sounds they are making through motor exploration such as mouthing toys.  For example, the sound produced changes when a child vocalizes with a toy obstructing their airway because they are mouthing it.  These sounds will change in different ways based on the size and shape of the toy being mouthed and allow babies early exploration of how to modulate the sounds they are producing.  A delay in reciprocating babbling is also a warning sign that a language delay may follow. 

Motor delays in acquisition of skills such as head control, trunk control, independent sitting, exploring toys in sitting with both hands and mouth, crawling, and walking can limit a baby's ability to achieve motor based early language, social interaction, and even cognitive milestones.  These limitations in other developmental areas demonstrate how motor skills shape early leaning in many other domains of development and highlight why many kids that are unable to achieve these motor milestones also show delays in other areas.