Her smiles, gurgles, giggles, and coos are more than simply adorable -- they're important milestones in your baby's development.

Your little one's first words or first steps are, of course, hugely momentous occasions. But experts say that the emotional milestones -- her first genuine smile or the first time she imitates your cooing -- may be more important to her development than physical achievements.

"Emotional interactions are the paths through which an infant learns about language and thinking," says Stanley I. Greenspan, M.D., a clinical professor of psychiatry and pediatrics at George Washington University Medical School in Bethesda, Maryland, and author of Building Healthy Minds. During the first year of life, your baby will go through these five emotional -- and exciting -- stages.

1. Curious George From birth to 3 months, your baby is gradually adjusting from an existence in a dark, calm womb to life in a bright, noisy world. Being able to stay relaxed amid all the chaos is your baby's first emotional task. You'll know he's reaching this milestone when he looks wide awake and concentrates on your face, peers into your eyes, even furrows his brow as if he's trying to figure you out. "You're getting to know each other, and it sets the groundwork for relating to others," says Mona Delahooke, Ph.D., a clinical psychologist in Arcadia, California.

What you can do: Holding your baby in your lap, let him grasp your finger and look at you as you gaze at him. Sing, talk softly, or make soothing sounds while you change his diaper.

2. Little Lover "Falling in love" is how Dr. Greenspan describes the period from 2 to 5 months when your baby gives you loving facial expressions and gestures, like patting your chest while she's nursing. "Your infant begins to show emotional intimacy; she looks at you with warmth and moves rhythmically with you when you rock her." At around 2 months, your baby will first smile at you in earnest. "She may smile before this age, but that's usually due to some physical satisfaction, like being fed," says Alan Fogel, Ph.D., a professor of psychology at the University of Utah, in Salt Lake City. "But now she'll light up just because you walk into the room. By 4 months old, her smiles will range from little grins to wide, open-mouthed expressions of joy. She may begin to giggle."

What you can do: Get to know the cues that tell you when she's overstimulated, anxious, or happy. Encourage her to imitate your expressions by smiling at her, frowning, even sticking out your tongue.

3. Funny Girl If it starts to sound like a barnyard around your home, you probably have a happy 3- to 6-month-old. Your baby is beginning to respond to you verbally, and she's watching for your reactions. If you say "aaah" to your baby, she may respond with "oooo." If you make a funny face or cover your face with your hands, then open them up and say "Boo," she may laugh.

What you can do: Engage her senses. Change the tone of your voice; give her toys with different textures; experiment with touch, from light foot massage to tummy raspberries.

4. Game Boy At around 6 to 9 months, your baby may start initiating play. He'll "talk" to you with sounds, facial expressions, and gestures. "This is the beginning of two-way communication," Dr. Greenspan says. "He's determined to convey his intentions to you. He now knows that his behavior will get a response from you and that what he expresses can have an impact. He's learned that he's a lovable being."

What you can do: If your infant coos at you, coo back, but then change the coo to an "aaah" to see whether he imitates you; if he says something else, like "eee," imitate him. "That's a circle of communication," Dr. Greenspan says. "You're extending the conversation, and your child is learning how to talk."

5. Little Sherlock Starting at around 9 months, your child can solve problems. "Being able to move around and stand up changes a baby's view of the world—she sees herself as a person who takes initiative," Dr. Fogel says. At about 12 to 18 months, your baby may pull you over to the refrigerator to get a snack, or she'll crawl and turn around to see whether you're following her. She wants to get your reaction, and she's making sure it's safe to continue.

What you can do: Let your child explore her surroundings, but let her know you're nearby if she needs you. Playing dumb helps your child's problem-solving skills: Put her favorite toy out of reach on a shelf, and say, "How are we going to get it?" If she pushes a step stool over to the shelf, praise her ingenuity.

Parents Magazine