Where in the Bible does it say that either Mary or Joseph had other children?
"While He was still speaking to the crowds, behold, His mother and brothers were standing outside, seeking to speak to Him. Someone said to Him, "Behold, Your mother and Your brothers are standing outside seeking to speak to You." (Matt. 12:46,47) "Is not this the carpenter's son? Is not His mother called Mary, and His brothers, James and Joseph and Simon and Judas?" (Matt. 13:55). Unless you reply on some gnostic tradition, the plain reading of the text is that Mary and her other, natural children came to visit Jesus.