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 is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
We have not come across a narration of the Prophet which clarifies the number of children of Aadam but the history books mentioned that he had 40 children.
Ibn Al-Jawzi said: "Hawaa' (Eve) gave birth to 40 children, boys and girls, from Aadam, in twenty pregnancies, and it is said that she was giving birth to twins each time, a boy and a girl. The first of his children were the twins Qabeel and Qaleemah, and it is also said that her name was Qaythamah, and his last children were twins Abdul-Mugheeth and Amatul-Mutheeth."
However, it is reported that Ibn 'Abbaas said that Eve's first son's name was 'Abdur-Rahmaan. Moreover, Imaam At-Tabari and Ibn Al-Atheer stated as well that the number of the children of Aadam was forty children, boys and girls.
For more benefit, please refer to Fataawa 83733 and 87711.
Finally, it should be noted that not knowing such matters does not harm in any way, and therefore a Muslim should be preoccupied instead in acquiring the knowledge of Islamic rulings, which if he did not know, he is harmed.
Allaah Knows best.