Sometimes married grad students ask me when is the right time to have children. After I get my degree? After my wife gets hers (or my husband gets his)? After I land a teaching job? After I win tenure? After I am established in my field? You see how it goes; the right time never comes.
My suggestion: Children change us. Don’t wait to have children when the right time has come; the time becomes right when you have them. If you were ready for marriage, you are ready for children. Stop waiting. Stop dithering. Just begin.