Physical Development

To climb, or not to climb? That, for many babies, is the question. It's not clear what makes some little ones climbers, while others prefer firm ground. But one thing is certain: When you come into the dining room and find your 9-month-old hanging from the back of a ladder-back chair, it's time to reassess your childproofing plans.

Unlike tree-dwelling mammals (i.e., squirrels and monkeys), human beings are not climbers by nature. Scaling mammals, as they are known, move their limbs appropriately for their habitats using reflex reactions. With human infants, the instinct to climb is sometimes there, but the skills must be learned--a task that some babies take more seriously than others. If your child is obsessively drawn to stairs and bookcases, chances are she's a climber. As soon as she can stand while holding on, she'll start using anything she can as leverage to pull herself up.

Social Development

Just as some kids love to climb and others couldn't care less, your baby's emerging personality may show up in a variety of new fears. Common phobias at this stage include fear of vacuum cleaners, the bathtub, thunder, and the dark--or your child may come up with her own. These fears are caused by the realization that the world is more complex, and therefore, more potentially dangerous, than previously thought. Offer reassurance and, where possible, practical solutions--a night-light, new toys for the tub, a "meet-and-greet" session with the vacuum when it's not being used. Be sympathetic, but keep it light, short, and sweet, and her anxiety will pass with time.

Intellectual Development

She may be less than 3 feet tall, but your child already has a distinct cognitive style. In an experiment at Harvard's Center for Cognitive Studies, 1- to 10-month-olds were briefly shown faces and balls in each of two windows. Some found faces more interesting, while some preferred balls, and others liked both equally. Reports from parents suggested that the babies who preferred balls were happier playing with toys, while those who liked faces were more content in social situations.

Other studies have shown that, from early infancy, some children operate with a master plan for reaching their goal--they learn maneuvers separately and put them together toward an end result. Others run through a roster of skills until they find one that works. The bottom line? Your baby has her own way of perceiving, understanding, and--ultimately--conquering the world.

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.