Can someone tell me how I decide what size racket to purchase? I love tennis, and used to "play" a lot but I'm sure I never used the right size. My 5 year old son wanted a tennis racket for Easter (isn't that surprising!!!) and I thought it be something really great to do together. I bought his based on the size in inches that was on the package but for adults, it pretty much just says "adult". You could clearly see that they were different sizes. I noticed on the side of the handle different sizes had different numbers, but no clue what they mean. Thanks a lot!