Babbling (repeating nonsense syllables) may begin. Susan Attiyah, of Glendora, Calif., tells the story of putting her 4-month-old down in an empty room for his nap. "My little 4-month-old son woke up and all by himself realized that if he would make a sound it would echo back," Attiyah says. "He spent 30 minutes talking (well, baby talking) and hearing it echo back to him and then he would giggle."

Your baby will let you know when you're doing something she likes by smiling, laughing and squealing in delight. She's also learning how to tell you when playtime is over. "Respect the baby's cues," Teitelman says. If she's turning her head away or getting agitated, give her the down time she's telling you she needs.

The baby's new awareness of the world and the most important people in it – his parents – means that the first bouts of stranger awareness and anxiety often occur during this period.

Your baby is not a helpless newborn anymore. He's beginning to learn to control his body and his movements. By 6 months, he will be lifting his head, holding it steady and doing modified push-ups. He'll probably begin rolling over at some point during this period. He may enjoy sitting up, and may actually be able to sit up without support.

Some babies start pulling up to stand near the end of this period. And some are early crawlers or creepers. "She is already crawling, or should I say hopping, across the living room," says Elizabeth Ferree, of Yuma, Ariz., of her 6-month-old. "Our ground is pretty hard so I do have to watch her."

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