6 weeks

The first six weeks can be a real trial. Hold on to the thought that right around that six-week mark you will be rewarded with one of the most gratifying milestones in your entire parental career--your baby will beam a genuine smile at you.
At 6 weeks, about half of all babies can recognize their parents, and many of those babies are so delighted that they welcome Mom or Dad with an excited, gurgly grin. This is one of the first signs that your baby is developing an ability to socialize. In fact, it's called a "social smile," and it's one of the more emotionally gratifying milestones you'll see your baby reach.
Now that your baby's awake for longer periods during the day, you can use these times to support his sensory development. Try singing your favorite lullabies or playing music.

You don't have to limit yourself to children's songs. Fill the house with the sounds of music — from the Black Eyed Peas to Mozart — and watch as your baby expresses his pleasure through coos, lip smacks, and jerking arm and leg movements.