Junior tennis racquets are best purchased using height, not age, as a guide. All children are different and grow at different times, so it's best to use the 1 inch rule - get the child to stand up straight holding the racquet down by their side. Ideally, there should be a 1-inch gap betwen the ground and the end of the racquet.
It's not a perfect science, and as long as the racquet is not touching the ground, you should be ok. It's better to have a smaller racquet than one that is too big, as bigger racquets are heavier and therefore could be harder for small arms to keep the racquet horizontal to the ground at the point of impact with the ball.
There is no need to overspend when purchasing a junior racquet in the smaller sizes as children tend to grow out of them within a year or so. You can't go too far wrong on brand, but the big 5 racquet manufacturers are Wilson, Head, Babolat, Prince and Yonex. Anyone of these would be great for your aspiring player!
As a general guide, use the table below to help you:
Height of child | Racquet length |
< 100 cm | 17 inch |
100 cm - 110 cm | 19 inch |
110 cm - 120 cm | 21 inch |
120 cm - 130 cm | 23 inch |
130 cm - 137 cm | 25 inch |
137 cm - 148 cm | 26 inch |
> 148 cm | 27 inch |