One of the most common questions I'm asked throughout the year is, "What advice do you have on buying a bat for my player?" While I rarely have the answer people think they're going to get--I don't believe that any one brand or model is better than any other--I do have three rules of thumb to keep in mind:
Lighter is better. No Little Leaguer of any age needs a bat that weighs more than 20 ounces. Tee Ballers should use a bat that is, at most, 15 ounces. We buy 16 ounce bats for our Rookies players, 17 ounce bats for our Minors players, and so on. As a general rule, remember the "drop-10" system, meaning that a bat should weigh ten ounces less than its length in inches. 25 inches, 15 ounces is a good Tee Ball bat; 30 inches, 20 ounces is a good bat for Majors players.
Spend wisely. The rules for bats change so frequently that spending more than $100 on a bat can be a risk. With the rate at which players grow, they'll need a new bat as often as every year. Remind your player that it's not the bat that does the hitting; it's the swing.