Part of Mary's calling I hadn't considered before

Just a brain tickler that I never pondered until recently -- doesn't part of Mary's calling to be the mother of God mean she had to accept that she would only have 1 child? Is there anything Catholicism says about this? Only children wouldn't have been that common for the time period or Jewish culture, so I imagine this would have been a harsh reality to accept as part of Mary's yes to God.