Are the kids considered as kids of Zina (adultery) if the father is not praying?

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

According to the preponderant opinion among Muslim scholars, a person who gives up prayers absolutely is considered a Kafir (disbeliever), i.e. he becomes a non-Muslim. But, his children are not illegitimate; they are traced back and attached to him as long as he has had legitimate marriage with their mother.
Sheikh al-Islam Ibn Taymiyah said: 'There is agreement among Muslim scholars that a child is to be traced to his father and is entitled to receive inheritance from his father and vice versa as long as his father has had legitimate marriage with his mother and consummated it with her'.
Allah knows best.