بسم الله الرحمن الرحيم
(Fatwa: 1029/836=L/1430)
If the woman does not marry any non-mahram of the children, she will have right to keep a son till 7 of his age and a daughter till 9 of her age. Then, the right of upbringing shifts to father or grandfather. So in the case mentioned above, she cannot claim to keep the son with her, but she can keep the daughter for more two years.
Allah knows Best!
Darul Ifta,
Darul Uloom Deoband
