There is no reason why women should not bring their children to the mosque with them in Ramadaan. The Sunnah indicates that women came to the mosque with their children at the time of the Prophet (peace and blessings of Allaah be upon him), because of the hadeeth: “I begin to pray and I intend to make it lengthy, then I hear the crying of a child and I make my prayer short, because I know that his mother is experiencing hardship because of his crying.” And: The Prophet (peace and blessings of Allaah be upon him) carried Umaamah as he offered an obligatory prayer whilst leading the people in prayer in the mosque. 

But they should try to protect the mosque against any najaasah (impurity) and being careful lest the children fall asleep in the mosque and so on. End quote