FOR THE PARENTS!!!
Having correctly fitted golf clubs for juniors is important for the development of the player. Clubs that are too heavy, too long (or short) or have incorrect lie angles can be very detrimental to your child's development. Heavy and long clubs often lead to a poor backswing, a flat and low take away then a lifting of the club to the top of the swing, this leads to poor swing shape and poor swing plane needing compensation moves.
Fitting the clubs is not a complicated science. It can be simply and accurately measured using a fitting chart, below is an example of US KIDS fitting chart. If buying custom fitted clubs is financially not an option then cutting down ladies clubs to fit is an option, the lie and weight of the club will not be ideal, but it's better than letting your child play with full size clubs too early. This picture shows the correct driver length for the junior compared to an adult driver length.