According to Islam, the expenditures of the children are the responsibility of their father, although who has custody may vary depending on their age and gender.
Imam Khomeini says: “The custody of the son until two years of age and the daughter till seven years of age is the right of the mother, and after that the mother no longer has any rights regarding their custody and the father can take the children from there on. Nevertheless, the expenditures of the children are the responsibility of the father from the beginning. Also, if the mother gets married to another person during the period that she has custody, she will lose her right and the father will take custody of the children from there on.”
Of course, during this time period, both the mother and father have the right to see their children.
Ayatullah Bahjat says: “During the time when the father or mother has custody of the children, if the other (who doesn’t have custody) wishes to see the child in order to give him/her something, solve his/her problems or just be beside him/her for a while, the other has no right to prevent such a thing from happening.”