Albert Barnes on Mark 2:5

Their faith. Their confidence, or belief, that he could heal him.

Son. Literally, child. The Hebrews used the words son and child with a great latitude of signification. They were applied to children, to grandchildren, to adopted children, to any descendants, to disciples, followers, young people, and to dependents. Mt 1:1. In this place, it denotes affection, or kindness. It was a word of consolation:--an endearing appellation, applied by the Saviour to the sick man, to show his compassion, to inspire confidence, and to assure him that he would heal him.

(g) "saw their faith" Acts 14:9, Eph 2:8