what is the best way to promote healthy brain development for infants and toddlers?

Have conversation with them:
 When an infant coos response with a delighted tone of voice. slowly draw out syllables in a high pitched tone say " Pretty Baby!" the talk is called "parentese" ( areas in the brain for understanding speech and producing language.

Play games that involve the hands:
Patty-cake, peekaboo, or this little piggy. Babies respond well to learning simple sequential games.

Be attentive:
When the baby points be sure to follow with your gaze and remark items, or events of interest to them. It confirms to your baby how important their interests and observations are to you.

Books:
choose books with large colorful pictures makes noises and point at pictures with your baby. elaborate on story lines and encourage your toddlers to talk about the books.

Use diaper time:
Touch your baby play with the hair rub the tummy studies show babies who aren't touched and played with often tend to have smaller brains.

Toys: 
Allow your baby to adore and interact with toys. something like a jack-in-the-box to help your child understand cause-and-effect sequences. Or blocks if your child stacks bigger blocks on smaller ones it will fall they can learn to put smaller on bigger.

Clean up:
have your toddler learn that stuffed animals have a place to go for night night time. Teach them where their things go to help them become more categorized.

Songs: 
sing songs like the itsy bitsy spider and ring around the rosey. The body motions and finger play will help your baby integrate sounds with large and small motor action.