When buying new ballet shoes it is worth checking
that they come with elastics.
When children/adults are dancing, the backs of the shoes can 'slop off' causing damage to the feet.
The sole of the foot can contract, when dancing, to assist in keeping the ballet shoe on the foot causing aching and painful feet, also problems learning to stretch the feet too.
It is not recommended that the drawstring will do for keeping the ballet shoe on as the tightness of the draw string could dig into the back of the heel.
It is important to sew elastics on immediately (or ribbons at the recommendation of your ballet teacher).