Balls:
Bats: Must be made completely from either wood or aluminum. Older, more competitive teams/leagues may not permit the use of aluminum but, until recently, this was fairly rare until the players reached the collegiate level.
Glove: Each player should have his or her own glove and should take the time to find one that is comfortable and fits well. Players, especially younger ones, should choose a smaller rather than larger glove, because a larger glove is more difficult to open and close quickly. T-Ball players might consider a vinyl glove, which are much softer and does not need to be broken in like a glove made of leather. Breaking-in a leather glove is a time consuming, but necessary task. Use softening oils or saddle soap, and tie a ball or two into the glove using rubber bands or string to form a well-defined pocket. Have your players repeatedly pound a ball into their glove while watching TV or, better yet, attending a high school, college or professional baseball game.
Apparel: Each player should have a shirt or jersey, knee-length or longer pants, baseball socks / stirrups, shoes with rubber cleats, and a hat to shield the hot summer sun from their face and eyes. The catcher will also have protective equipment, including a helmet, facemask, throat guard, chest-protector, protective cup (this is NOT optional) and shin guards. All other male players should consider wearing a protective cup, especially those in contact with the ball and sliding opponents often.
Bases: These may be supplied by your association or league, but regardless, be sure your league uses breakaway bases [6]. If they don't, do your best to encourage their use, since a large percentage of baseball injuries occur during sliding.
Links:
[1] http://www.ipsm.org/publications/softball_injuries/head.asp
[2] http://www.ipsm.org/
[3] https://mail.momsteam.com/node/134
[4] http://www.ipsm.org/publications/softball_injuries/blunt.asp
[5] https://mail.momsteam.com/node/301
[6] https://mail.momsteam.com/node/283