Mantra for a Child

This mantra may be recited for getting a son, or for childless couples, who want a child.

Devaki-sut Govinda Vasudeva Jagatpate
Dehi me tanayam Krishna Tvaamaham sharanam gataha

O Son of Devaki and Vasudeva, the Lord of the Universe
O Krishna! give me a son; I take refuge in you

As such, the result is up to the Lord.  We do our best, but in the end, He knows what is good for us.  I cannot promise that this mantra will work, but faith is known to move mountains.