Physical Development

Somewhere between the fourth and sixth month, the pediatrician will suggest starting your baby on solid foods. Although it's tempting to move into this phase as soon as possible--after all, he's going to look so darned cute with that bowl of spaghetti on his head--don't rush to introduce solids. The older he is, the less likely he'll suffer allergic reactions. In addition, babies younger than 4 months of age have trouble digesting complex foods such as cereals that contain starch.

You'll know your baby is ready for solids when he can sit well, with support, and hold his head up; when he can swallow (a decrease in drooling is the tip-off here); when he's doubled his birth weight; and when he's lost the tongue-protrusion, or gag, reflex. He'll also show an increased interest in the food on the table, trying to taste things off your plate or even smacking his lips when he sees you eating. We'll talk more about solids next week.

Social Development

Although crying has probably decreased dramatically by this point, it's still your baby's primary mode of communication. He'll cry when he's tired or lonely, wants attention, or is ready for play. (He'll also sob poignantly when you leave him, but don't worry--he'll generally be fine as soon as you get out the door.)

In the morning, he'll wake up hungry but may vocalize to himself for awhile before the discomfort becomes acute. If you pick him up before he starts wailing, he'll anticipate feeding and wait a little longer before losing control. But his patience is limited: If he doesn't eat within a few minutes, he'll quickly become agitated.

Intellectual Development

Your little one now has responsive periods of an hour or more at a time. He's applying the information he's absorbed over the past few months to his day-to-day activities, and has coordinated his perceptive and motor skills to the point where he can play alone for longer periods. He loves toys, using them to learn about spatial relationships, color, texture, and cause and effect. But he loves socializing even more--although he tires of toys, he never gets bored with your attention.

Note: The information above offers general guidelines, but all babies develop differently, and few hit their milestones precisely when the conventional wisdom says they should. If your child was born prematurely, you may want to use your due date as a baseline for following baby's development.