There are 4 types of balls as generally recommended by ITF and other Tennis bodies and coaches. These are identified by their color and prescribed for different stages of kids development.
Red balls are for very young kids (4-7 years), who are just starting out and probably useful for establishing the hand eye coordination. Red balls Tennis courts are also half of the size of normal courts.
Orange balls are for next stage (7-9 years), which have around 50% compression of normal balls, resulting low bounce. The court size are also 3/4th of normal court size.
Green balls are official balls for all under 10s tournaments. These are 75% compression level. The court is though full size for them.
Normal balls, also called Yellow Balls, are for anything for and above under 12s. There are different Yellow balls specialized for a given type of court like Hard court or synthetic grass or clay, etc.
Tennis associations and coaches put lot of emphasize on using correct stage of balls. We started with Yellow balls, but my son’s coach insisted on using Green balls as they were proper for his age.
One benefit of playing Green (or any stage) balls I have seen is that kids learn to spin and control well as they have more time to play the ball plus they don’t bounce above the shoulder.
My main issue with Green balls is the lack of true momentum in the ball, which makes it difficult to transition from Green to normal Yellow, as the feel is way different.
I think if you are happy with kid’s swings technically, it may be better to use normal Yellow balls. Its kind of hard for me to see any great benefit of using stage balls (Red, Orange or Green), but Tennis experts and coaches think its a good thing in a long run. They may be right ! I don’t know.
My son is using both Green and Yellow for practice with more and more Yellow. Yellow balls expose another set of challenges for him which are not there with Green balls. For example faster feet movement; timing the ball (as Yellow balls have different momentum); etc.
The Yellow balls also demand more of his athletic abilities than Tennis skills. Its beginning to get more physical for him and he is starting to feel that. If he can survive this and still be interested in Tennis, he will come out good.
Finger crossed 🙂