Madonna of the Chair by Raphael Sanzio 1518
The young child behind Mary and Jesus is St. John the Baptist.
A priest on EWTN said that St. John received a special grace at the time when he leapt in his mother's womb at the meeting of Jesus in Mary's womb, that removed his original sin that he was conceived with, thus making him the greatest man ever born. Of course Jesus was greater but he was both God and man. Jesus said in the bible, "Truly I say to you, among those born of women, there has not arisen anyone greater than John the Baptist." Matthew 11:11
Maria Montessori said this about the work, “The children, of course, cannot comprehend the symbolic significance of the "Madonna of the Chair", but they will see something more beautiful than that which they feel in more ordinary pictures, in which they see mother, father, and children. And the constant companionship with this picture will awaken in their heart a religious impression.”