Your sweet bundle of joy has turned into a babbling ball of energy by the time he hits the 4 to 6 month mark. You've built a strong bond with your baby since birth, but most of your activities have been passive—your little one learned how the world worked from the safety of your arms. Now, the time has come for more proactive play.

Cuddling and cooing are still beneficial for your baby, but you'll need to add more "contingency" activities to your daily routine as your baby develops. Contingency play simply means that your little one likes to make things happen. "It's not just that young babies can benefit from such things; it's also that they are genuinely eager for the experiences," says Dr. Linda Acredolo, author of Baby Minds: Brain-Building Games Your Baby Will Love. "Most parents are surprised to learn that babies are born wanting challenges—eagerly trying to figure out how things work."

It's also time think outside the box—or the playpen, or high chair. Your baby's becoming much more physical and he needs to move his muscles. Most children in the 4-6 month age range can control their heads, roll over and kick and reach with a purpose. Physical and cognitive skills are tightly connected and activities that incorporate both types of challenges are crucial. To boost both body and brain try these simple activities:

  • Tummy time. Place your infant on his stomach on a blanket, and sit in his line of vision with some attractive toys. Try to entice him with shiny or noisy objects. He'll lift his head, and possibly start rocking his body. His arms and legs will kick freely with interest and excitement. This type of play allows your baby to practice controlling his head, limbs and body movements. This kind of stimulation without restraints is a necessary precursor to crawling, and hones fine motor skills. Practice but don't push—let your baby go at his own pace.
  • Read my lips. Your baby has started to babble, and it may come as a surprise that sight is just as important as sound to your budding language learner. In a recent Florida Atlantic University study, researchers learned that babies look at lips when they hear someone talking. The infants continue to concentrate on that area of the face until they begin talking fluently at about 12 months. Hold your little one in a comfortable position where he can focus on your mouth and lips, talk to him and respond to his sounds. Speaking back to his coos while he gazes at you will help speed and strengthen language development.
  • Fun with fingers. Fine motor skills are improving at this age—your baby likes to reach for things and hold on tight. Give your baby safe objects to grasp, such as your index finger. Pretending that you're "caught" by baby will leave him tickled with delight. Also, hand over toys that are small enough to fit in a little fist, but not so tiny that your baby can get them in his mouth to swallow, or possibly choke on.
  • Baby's day out. Begin planning educational, child-centered outings and let your little one lead the way—at least some of the time. Point out the colors and shapes of fruits and vegetables at the grocery store, or take a trip to the zoo and name the animals. Stay tuned to your baby's interests, and shift your focus on the bird that catches his eye—even if you want to tell him all about elephants. If he's zoned in on a particular object, he'll delight in learning about it.
  • Cause and effect. Plan some serious peek-a-boo time. Your baby has always loved to look at your face, but now he wants to know that he's in control. Instead of using your hands, take a towel or scarf and put it over your face, and then let your little explorer pull it off. Or hide behind something and wait for your baby to make a sound before you come out. This teaches the basics of cause and effect and gives your tiny tot confidence in his abilities to manipulate the world around him. Try the same thing with toys—hide a truck under a cloth, and then let your child discover it himself.
  • Book buddies. If you're not, it's time to begin reading to your baby. Letter and word recognition are still a long way off, but establishing a reading routine can get your budding bookworm comfortable with stories and language. Prop him on your lap, read slowly from board books, and let your little one reach for the pages—he may even want to grasp or chew the books. This is a great way to build a foundation for a lifelong love of learning and reading.

Remember, you're still an essential part of your baby's learning experience—it's not time yet to let him play alone. Your infant is growing rapidly and he craves experiences where he can succeed. "Every time a baby succeeds at something, connections are made in the brain that make it easier for similar conquests to occur the next time around. That's what 'learning' is, after all," says Dr. Acredolo. Set the stage for these challenges in a safe way, and your baby will reap the rewards for years to come.