Glove

Choosing the right size glove for your T-Ball or Coach Pitch player is so important. Depending on your child’s hand size, glove sizes for ages 3 to 6 years are between 8 and 11 inches in length.
Here is a great option from Mizuno

Bat

Whether you are starting out in T-Ball or Coach Pitch, the bat size for your beginner is basically the same. The average length of bats for 3–6 years are 24–27 inches. The weight may also vary anywhere from 13 to 17 oz. Bats must have the USABaseball stamp on them.
Here is a great option from Rawlings

Helmet

Another essential piece of equipment for both T-Ball and Coach Pitch is a batting helmet. There are many different options of helmets including color, face mask (required), and ones with a detachable chin strap.
Here is a great option from Easton