All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
If the deceased did not leave any heirs entitled to inherit except those mentioned in the question, then the mother gets one sixth of the estate as a fixed share because the deceased has children. Allaah, The Exalted, says (what means): {And for one's parents, to each one of them is a sixth of his estate if he left children} [Quran 4:11]
The husband gets one fourth of the estate as a fixed share because the deceased has children. Allaah, The Exalted, says (what means): {But if they have a child, for you is one fourth of what they leave, after any bequest they [may have] made or debt} [Quran 4:12]
The remainder of the estate is divided among the son and daughter by Ta‘seeb (i.e. by virtue of having a paternal relation with the deceased and not having an allotted share in the estate); the male gets double the share of the female. Allaah, The Exalted, says (what means): {Allaah instructs you concerning your children: for the male, what is equal to the share of two females…} [Quran 4:11]
Thus, the estate should be divided into thirty six shares; the mother gets one sixth (six shares), the husband gets one fourth (nine shares), the son gets fourteen shares, and the daughter gets seven shares.
Allaah Knows best.