What major principle which govern the Court in the decision for custody of children?

The major principle which governs the Court in the decision for custody of children is the Welfare of the Children. Section 125(2) of the Law of Marriage Act, 1971. 

Note: other consideration are in section 125(2)(a)-(c) of the Law of Marriage Act, thus: 

1). Wishes of parents; 

2). Wishes of the child, if can express independent opinion; and 

3). The Customs of the community to which parties belong.