Hello Grace......The decision to have children or not is an individual and personal choice. My response as their mother would be one of support and understanding, as with the vast majority of their choices.
Being a parent is simply not for everyone and there is absolutely no reason for a young couple to feel a sense of obligation to bring a child into the world, once they have made a choice they feel is best for them.
For quite a while I believed my eldest son & his wife would be childless and I respected this without question. They owed me no explanation and it simply was never an issue for discussion.
For years they were focused on their careers and their marriage, with no desire to include a child.
After several years of establishing their lifestyle as they chose and having very successful careers, they then decided to have an only child, my precious grand daughter. My son finally became a Dad at age 40, his wife just a couple of years younger and they are perfectly content with this. As for Grandma, i WAS THRILLED, but certainly would have been happy for them, regardless of their choice.