Baby This Week: 15 Weeks Old

By now your baby has gone from being a passive observer of the world to being — or at least wanting to be — an active participant. Some babies this age even like trying to "stand." If your baby seems to want to stand up while being held securely on your lap, it means those little leg muscles are probably sturdy enough to explore this new sensation.

Your baby is starting to draw conclusions about the world around her. She's looking at everything with curiosity, even her own reflection.

Prop an unbreakable mirror next to her or set her in front of your mirror when you're getting ready in the morning. Your baby won't realize that it's actually her image in the mirror (which usually begins to happen well into the second year), but that doesn't matter. She'll love staring at her — or anyone else's — reflection, and she may show her delight with an all-out gummy grin.

At last, your baby's sleep patterns may start to settle down, giving you some rest. Many 4-month-olds sleep for a six-hour stretch through the night, though others still wake for an occasional feeding. Some babies take until age 6 months or later to sleep through the night, though, so don't get your hopes up! Two daytime naps are usual now.

Your baby may stop to listen to your voice. By cooing or making noises at her, and by describing even the most mundane household chore, you're not only connecting with her but also encouraging her to express herself. Wait and see if she "answers."

Your baby is becoming more animated and engaging (even with others) — flashing smiles, oohing, and cooing. And the fun has really begun as she's starting to laugh.

When you're with friends, keep your baby nearby so she can hear the richness of human interaction. She'll enjoy watching the antics of other babies, toddlers, and pets, but keep up your guard: Neither she nor they know the rules of safe engagement just yet.

Anything within your baby's reach is fair game now. While she's mastering her grabbing skills, give your baby interesting things to hold: lightweight rattles that are easy to grasp, a plastic or rubber ring to hold with both hands, squeaking toys, or soft stuffed animals.

Your baby will start to favor one hand for a while and then switch to the other, but you can't really tell whether she's a lefty or a righty until she's about 2 or 3 years old.

- BabyCenter.com