Physical Development

The nine-month checkup is likely to be a bit more traumatic than previous visits, due to your baby's increased sensitivity to strangers. In addition to a physical examination and any vaccines that haven't been done before (probably hepatitis B and a skin test for tuberculosis), the pediatrician will assess your little one's development and ask questions about sleep patterns, teething, progress toward walking, vocalizing, and diet. This is a good time to discuss weaning from the breast and/or bottle. Most pediatricians recommend cutting back to one or two bottles a day by around baby's first birthday, although nursing may go on far beyond that point.

Social Development

Your baby's increasing ability to get around makes this a difficult time for siblings, especially toddlers, who may see her as a personal threat. Older children may find it difficult to believe that baby is too young to understand sharing or appropriate boundaries, and may retaliate by pushing or hitting her, giving her disgusting things to eat, or trying to lock her in the closet. Although unpleasant, these interactions have value: Baby learns self-protection and becomes proficient at reading her siblings' moods, while older children vent negative feelings and gain access to positive ones. Rather than stifling these exchanges, try channeling them into games such as roll-the-ball (sibling throws ball for baby to fetch). Don't intervene when conflicts arise unless baby is in danger of being harmed. And of course, never leave little ones alone with children under the age of 10.

Intellectual Development

You may notice that your child is becoming aware of vertical space. She may suddenly be afraid to enter her high chair, or cry when you hold her above your head. To allay this anxiety, many babies practice falling by repeatedly pulling themselves to a standing position, then dropping to their knees. She may even drop a favorite toy from her high chair or the top of the stairs, then attempt to climb down and console it--an early sign of symbolic thought.

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.