Child developmental Milestones Infants One to Four Months

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Developmental Milestones - Infants One To Four Months


  • average length is 20 to 27 inches; grows approximately 1 inch per month
  • weighs an average of 8 to 16 pounds (females weigh slightly less than males)
  • gains approximately to pound per week
  • respiration rate is approximately 30 to 40 breaths per minute; increases during periods of crying or activity
  • normal body temperature ranges from 96.4 to 99. 6 F (35.7- 37.5 C)
  • head and chest circumferences are nearly equal
  • head circumference increases inch per month until 2 months, then increases 5/8 inch per month until 4 months (increases are important indications of continued brain growth)
  • heart rate is approximately 120 to 150 beats per minute at rest
  • continues to breathe using abdominal muscles
  • posterior fontanel closes by second month
  • anterior fontanel closes to approximately inch
  • skin remains sensitive and easily irritated
  • arms and legs are of equal length, size and shape; easily flexed and extended
  • legs may appear slightly bowed
  • feet appear flat with no arch
  • cries with tears
  • eyes begin moving together in unison (binocular vision)
  • color vision is present


  • reflexive motor behaviours are changing:
  • tonic neck and stepping reflexes disappear
  • rooting and sucking reflexes are well-developed
  • swallowing reflex and tongue movements are still immature; continued drooling and inability to move food to the back of the mouth
  • landau reflex appears near the middle of this period; when baby is held in a prone (face down) position the head is held upright and legs are fully extended
  • grasps objects with entire hand; strength is insufficient to hold items
  • holds hands in an open or semi-open position
  • muscle tone and development is equal for boys and girls
  • muscle strength and control is improving; early muscle movements are large and jerky; gradually become smoother and more purposeful
  • raises head and upper body on arms when in a prone position
  • turns head to side when in a supine (face up) position; near the end of this period the head is held erect and in line with the body
  • upper body parts are more active; clasps hands above face, waves arms about, reaches for objects
  • infant rolls from front to back by turning head to one side and allowing trunk to follow; later rolls onto its side. Near the end of this period, the infant can roll from front to back to side at will
  • can be pulled to sitting position with considerable head lag and rounded back at the beginning of this period. later, can be positioned to sit with minimal support. near the end of this period, the infant sits with support, holds head steadily and keeps back fairly erect; enjoys sitting in an infant seat or being held on a lap


  • fixates on a moving object held at 12 inches; smoother visual tracking of objects across 180 degree pathway, vertically and horizontally
  • continues to gaze in direction of moving objects that disappear
  • exhibits some sense of size, color and shape recognition of objects in the immediate environment
  • does not search for a bottle that falls out of a crib or for a toy hidden under a blanket
  • watches hands intently
  • moves eyes from one object to another
  • focuses on small object and reaches for it; follows hands' movements with eyes
  • alternates looking at an object, at one or both hands, and then back to the object
  • imitates gestures that are modeled
  • localizes the source of sound
  • connects sound and rhythms with movement by moving or jiggling in time to music, singing or chanting
  • can distinguish parent's face from stranger's face when other cues such as voice, touch or smell are also available
  • attempts to keep toy in motion by repeating arm or leg movements that started the toy moving in the first place
  • begins to mouth objects


  • reacts to sounds such as a voice, rattle of a spoon, ringing of a bell
  • coordinates vocalizing, looking and body movements in face to face exchanges with parent or caregiver; can follow and lead in keeping communication going
  • babbles or coos when spoken to or smiled at
  • produces single vowel sounds (ah, eh, uh); also imitates own sounds and vowel sounds produced by others
  • searches for source of voice (turns head, eyes look for the speaker)
  • laughs out loud


  • uses eyes to imitate, maintain, terminate and avoid interactions
  • reacts differently to adult voices, may frown or look anxious if voices are loud, angry or unfamiliar
  • enjoys being held and cuddles at times other than feeding and bedtime
  • coos, gurgles and squeals when awake
  • smiles in response to a friendly face or voice
  • can entertain self by playing with fingers, hands and toes
  • enjoys familiar routines, such as being bathed and having diaper changed
  • delights in play that involves gentle tickling, laughing and jiggling
  • spends much less time crying
  • recognizes and reaches out to familiar faces and objects; reacts by waving arms and squealing with excitement
  • stops crying when parent or caregiver comes near


Check with a health care provider or early childhood specialist, if by four months, the child does not:

  • continue to show steady and measurable increases in height, weight, and head circumference
  • smile in response to the smiles of others (the social smile is a significant developmental milestone)
  • follow a moving object with eyes focusing together
  • bring hands together over mid-chest
  • turn head to locate sounds
  • begin to raise head and upper body when placed on stomach
  • reach for objects or familiar persons

The information provided should be used as a general guideline and for general information. Children are unique individuals. No two children grow and develop at the same rate. If you have any questions concerning your child's development, contact your pediatrician.

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