Racquets come in all shapes and sizes.
The standard length for an adult racquet is 27 inches. A junior should use as long a racquet as she or he can comfortably handle.
If it is too small, the player will have to use excessive wrist and elbow action - which is bad for technique and the arm.
Once a junior weighs about six stone (38 kg), they are ready for an adult racquet.
Go for a light racquet; which makes it is easy to handle.
Age 0-4 years: 19"
Age 4-6 years: 21"
Age 7-8 years: 23"
Age 9-10 years: 25"
Age 10-12 years: 26"
Age 12 years plus: 27"
If it is too light, too much vibration will be transmitted to your arm.
Between 10 and 11 ounces (280-300g) - about as light as a packet of biscuits - should be a good choice for a beginner.