1) you will have to make application for child custody at court in Delhi where the child is currently residing
2) since child is only 6 years old court may not award you child custody
3) court would grant you visitation rights for the child
4) it is your case that mother had converted into islam before marriage
5) As per Muslim personal laws, minor children are given to mothers. But after the age of seven years, the mother’s right over the son ends. Girls are given to mothers until they attain puberty.the conduct of the mother is of great importance, and if that is found ‘objectionable’, she may not be given custody rights. The father has the right to custody after the mother’s term ends.