Weight. Average gain of 1 to 1¼ pounds each month; by 4 to 5 months has doubled birth weight

Height. Average growth of ½ to 1 inch each month

Head size. Average growth of about ½ inch each month

Grasp, Moro, root, and tonic neck reflexes (reflexes normally present in young infants) disappear

Balances head well

Leans on hands to support when sitting

Pushes up with straight arms when on tummy

Rolls from tummy to back by 6 months

Starts drooling (not always a sign of teething)

Naps 2 to 3 times a day, for 1 to 3 hours each (on average)

Starts to sleep longer at night (6 to 8 hours consistently)

Has full-color vision, able to see at longer distances

Takes turns making sounds with you

Laughs

Squeals

Blows bubbles or "raspberries"

Knows familiar things and people

Puts things in their mouth to explore them

Reaches to grab a toy they want

Closes lips when they don't want more food

Likes to look at self in a mirror

Repeat sounds and smile when your baby makes sounds.

Laugh with your baby.

Talk to and imitate your baby during feeding, dressing, changing diapers, and bath time.

Spend time on the floor playing with your child every day.

Dance with your baby and do other rhythmic movements.

Introduce your baby to other children and parents.

Place safe toys near your baby to encourage reaching and grasping.

Encourage laughing and play by making funny faces or sounds or blowing on baby's belly and laughing.

Play peek-a-boo games to help develop object permanence, the understanding that objects are still present even though they can't be seen.

Show your baby bright picture books and interesting objects.

Show your baby their reflection in a mirror.

Read books and stories to your baby, and point out pictures.

Take your baby outside to see new things and people.

Hold your baby for feedings and cuddle when they are awake.

Hold and comfort your baby when they are unhappy.