Perhaps the primary reason why it is important for children who perform dance routines to have new dance costumes is to augment their confidence. When a child goes on stage with a beautiful costume that fits like a glove, it removes all fear or anxiety about wardrobe malfunctions. New costumes are often tailor-made, while secondhand costumes can fit less well as they were most likely made for someone else. Confidence will show in every aspect of the child's performance.
For child dancers, and for those who participate in dance competitions in particular, the importance of new dance costumes is paramount. Historically, part of the enjoyment of a dance performance is the visual effect of beautiful costumes onstage. Often, new costumes are the most dynamic given their unworn, untarnished state. For young competitive dancers, the importance is even greater -- often a component of a routine's final score is directly related to the costume.
A new dance costume is simply more practical than a secondhand one. While it is true that new dance costumes can cost more than used ones, often, that price difference is made up for by the costs of repairs and alterations on a secondhand costume. A new dance costume arrives perfectly sized for your child, with all the buttons, straps and sparkles where they should be. Secondhand costumes often require significant work to get them up to par.
Consider your child's pride when weighing the importance of new dance costumes. Will your child be the only ballerina in the class with a secondhand tutu? Will it look the same as the other girls'? Children who dance often take great care and pride in their costumes, and a new dance costume is a special item that belongs only to her.