Martha Washington was a formidable woman, the trustee for her children of her late first husband Daniel Custis's 300 slaves and five plantations. Combined with the land and slaves she inherited from her father, she controlled about 27 square miles of land. She managed this little empire well, and so when George Washington asked for her hand in marriage in 1759 he knew he was getting someone who would be a great partner in whatever ambitions he might have. Indeed, he tripled the size of his Mount Vernon estate during his marriage to Martha, who herself kept the lifetime use of 1/3 of the Custis inheritance.

Washington and Martha, by all accounts, had a warm and loving marriage. They certainly knew how to have children, and they certainly tried, and as late as 1784, when George was 52 and Martha was 53, Washington may still have hoped that he might have a child of his own (emphases Washington's):

If my Commission is not necessary for the files of Congress I should be glad to have it deposited amongst my own Papers. It may serve my Grand Children some fifty or a hundd years hence for a theme to ruminate upon, if they should be contemplatively disposed.

Of course, we don't know exactly why they never had children. Martha may have suffered an injury during childbirth. Perhaps a life on horseback reduced Washington's fertility. In any case, we do know he genuinely loved Martha, and her children. After the death of his stepson John Custis in 1781, Washington adopted Custis' children as his own (one of whom bore the name George Washington Custis in his honor), and so it's also very possible he simply meant these children when he referred to his grandchildren.

Hey there,

Just to let you know, your question is fine, and we're letting it stand. However, you should be aware that questions framed as 'Why didn't X do Y' relatively often don't get an answer that meets our standards (in our experience as moderators). There are a few reasons for this. Firstly, it often can be difficult to prove the counterfactual: historians know much more about what happened than what might have happened. Secondly, 'why didn't X do Y' questions are sometimes phrased in an ahistorical way. It's worth remembering that people in the past couldn't see into the future, and they generally didn't have all the information we now have about their situations; things that look obvious now didn't necessarily look that way at the time.

If you end up not getting a response after a day or two, consider asking a new question focusing instead on why what happened did happen (rather than why what didn't happen didn't happen) - this kind of question is more likely to get a response in our experience. Hope this helps!