Mary had no other children after Jesus was born and the scriptural evidence of this is overwhelming.
1. Scripture never says that Mary had other children. We can only infer this on account of Scriptural references to brothers and sisters of the Lord. But nowhere were they referred to as children of Mary.
2. Reference to brothers and sisters would certainly include the possibility that these people were "half siblings", i.e., children of Joseph by an earlier marriage. In fact, this belief prevailed in the early church until the time of Jerome (d. 420). Jerome concluded that these brothers and sisters were in fact cousins. In Hebrew and Aramaic there was no word for "cousin" and the relationship was either designated "brother" or it was shown by circumlocution, such as "son of my father's brother", etc. For example, Genesis 14:14 (KJV) refers to Lot as Abram's brother; in Genesis 29:15 (KJV) Laban calls Jacob his brother; in 2 Kings 10:13-14 (KJV) the 42 captives of Jehu call themselves brothers of Ahaziah. Indeed it is possible that some of the "brothers" of Jesus were half-brothers and others were cousins.
3. When the angel announced the coming birth of the King of Israel, Mary's response was, "How shall this be, seeing I know not a man?" The implication here is that Mary had already committed herself to remain a virgin. The angel did not say when this birth was to take place and Mary was espoused to Joseph at that time. If she had planned on having sexual relations, she would be doing so shortly and it would not be a mystery how the birth was to occur. However, if she planned on remaining a virgin all her life, her question to the angel was perfectly understandable.
4. In the episode where the parents of Jesus found Him in the temple at age twelve, there is no mention of other children and if there had been other younger children they likely would have been mentioned.
5. None of the early church fathers advocated that Mary had other children. On the other hand, many of them advocated her perpetual virginity. Of particular note among this group were Jerome, Ambrose of Milan (d. 397) and Augustine (d. 430).
6. The early reformers, including Martin Luther, John Calvin and John Wesley all advocated the perpetual virginity of Mary.
7. The strongest indicator that Mary had no other children is contained in John 19:26-27, where Jesus places the care of his mother with John. If Mary had other children, this would have been unthinkable at every level imaginable. Some say Jesus entrusted his mother to John because His “brothers” were not believers at the time. However, this really is an attack on the prescience of Christ. Being the Son of God, He would have known that these brothers would become believers shortly after His death.
The only difficult Scripture for those who advocate the perpetual virginity of Mary is Matthew 1:25 ("but [Joseph] kept her a virgin until she gave birth to a Son"). The implication may seem to be that Joseph had sexual relations with his wife after the birth of Jesus. But the language of the Bible does not bear this out. For example, consider 1 Corinthians 15:25, "For He must reign until He has put all His enemies under His feet." Should we infer that He ceases to reign after He has put all His enemies under His feet? Likewise, we need not infer that Joseph had sexual relations with his wife after the birth of Jesus.