When my neice was born few elderly people did not let her mother to use new clothes for the newborn. Infact they went against her wish and choose torn old clothes for the newborn as her first clothes after coming in this world. What according to islam should be a newborns first clothing.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.

It is permissible to use new clothes or old ones for the newborn, or anybody else. It is not permissible for anyone to prevent the mother from clothing her newborn child in new or old clothes that she has at hand.

If some people have traditions in this regard, the mother is not obliged to follow them in their traditions as there is no evidence in Sharee'ah to support them.

Allaah Knows best.