All About SingleMother : Baby 4 Month Development ( fisher-price.com )

How your 4-month-old might play now

Rattles and teethers

Shake it. Place a rattle in baby's hand and gently shake it. Your baby will probably be interested in grabbing, shaking and dropping it.
Hear that? Help baby exercise coordination skills by holding a toy in front, shaking it, and letting him reach for it. Put the rattle in baby's hand, shake it and say, "Hear that sound? You did that!" Emphasizing the reward will make him want to try again.
Hand to hand. Choose a rattle that's big enough to let baby hold on with both hands. Place it in baby's hand; she'll grab on with one hand, then the other, and then let go. This action will develop into the skill of being able to pass an object from hand to hand.

Mobiles

Music, please. Extend the benefits offered by a mobile's music by playing music for baby at other times of the day and in different settings.
Sing or hum along. You'll find that as you do, your baby becomes more vocal too.
What do you see? Try looking at the mobile from baby's point of view. Change its position once in a while, or change your baby's position so she gets a new view.
Make the connection. Right from the start, your baby will listen to and respond to your voice. Use this connection to point things out about the mobile—the colors, the movement, the characters that dangle from it.

Soothers

Calm down. Help your baby learn to self-regulate—to stop crying and calm down. A soother with gentle sounds, music and sights helps baby understand when it's time to wind down and go to sleep.
See that? Point out the motion and lights to help baby focus on them.
So peaceful. Switch through the sound settings until you find one that's especially soothing to you and baby, then take a few minutes for yourself: listening to the soothing sounds as baby drifts off can be a peaceful time for you, too.

Infant play gyms

What do you see? Get down at floor level to get baby’s view of overhead toys. This will help you know where to position her for the best vantage point. Change your baby's position every once in a while to freshen the view.
Play together to encourage communication and add fun to playtime. Pick a time when baby is in an active play mode, not sleepy or hungry or overly stimulated. You'll be able to tell; if the toy looks too busy for him at the moment, he'll close his eyes.
Talk about it. To help your baby learn there's a connection between words and actions, move the parts and talk about them as you go: "Shake-shake-shake. See the silly little face smiling at you?"
Hum or sing along to the music on the gym and point out light-up features. The more you talk to your baby and directly engage him, the more you're benefiting his development.

Playard toys

Colors and high-contrast patterns are a great way to stimulate your baby's visual sense. Point out the colors and name the animals; even though your baby won't understand the meaning yet, she’ll learn that she can switch her focus, too.
Did you hear that? If a toy plays sounds, take advantage of this opportunity to stimulate your baby's sense of hearing. Take baby's hands in yours and gently clap them together to the music. Make expressive faces as you playfully sing along or imitate the sounds.