According to the majority of scholars, it is not permissible to break the obligatory prayers to answer the calls of one’s parents.

As for the voluntary prayers, it is permissible to break it to answer ones mother, as evidenced in the hadith of Jurayh Al Aabid whose mother called him whilst he was praying, and he didn’t answer her, so she prayed against him. The same applies to the father who calls his son during prayer. In fact the Imam al-Harmain said: “He should answer them even if it is an obligatory prayer and there is enough time still remaining left to pray it”. 

It is not allowed to reply to them whilst praying by saying: I am praying. If one does so, the prayer has been broken, and the evidence for this is a hadith by Muslim: “Talking is not befitting during the Salat (prayer), for it (prayer) consists only of glorifying Allah, declaring His Greatness and the recitation of the Qur’an.”