Luke 1:11 Just then an angel of the Lord appeared to Zechariah, standing at the right side of the altar of incense. 12When Zechariah saw him, he was startled and gripped with fear.
13But the angel said to him, “Do not be afraid, Zechariah, because your prayer has been heard. Your wife Elizabeth will bear you a son, and you are to give him the name John. 14He will be a joy and delight to you, and many will rejoice at his birth, 15for he will be great in the sight of the Lord. He shall never take wine or strong drink, and he will be filled with the Holy Spirit even from his mother’s womb. 16Many of the sons of Israel he will turn back to the Lord their God. 17And he will go on before the Lord in the spirit and power of Elijah, to turn the hearts of the fathers to their childrena and the disobedient to the wisdom of the righteous—to make ready a people prepared for the Lord.”
18“How can I be sure of this?” Zechariah asked the angel. “I am an old man, and my wife is well along in years.”
19“I am Gabriel,” replied the angel. “I stand in the presence of God, and I have been sent to speak to you and to bring you this good news. 20And now you will be silent and unable to speak until the day this comes to pass, because you did not believe my words, which will be fulfilled at their proper time.”
Perhaps they prayed to have a son when they were younger.