A/N: This is an essay reflecting my views on what should/will happen in the Book 7, and here's a hint: there's some things in here that will show up in Life As A Weasley...
I believe in the seventh book Molly and Arthur will either a) finally be blessed with grandchildren or b) have another child of their own. I tend to lean more towards option b as Bill and Fleur will just be starting their lives as a married couple. I also believe that Bill and Fleur aren't going to want to have children right away, for several reasons. Bill seems like the type who wants to fight the war at all costs, but he wouldn't even think about raising a family during wartime. Fleur also seems way too self conscious about her looks, so I'm willing to say she isn't going to want to ruin her figure anytime soon for child birth.
Charlie is in love with his job working with dragons, and probably enjoys the dragons more than he does chasing women, trying to find one to settle down with. He is also very passionate about the war and finding a wife is probably the furthest thing from his mind. Percy still hasn't fully come to terms with his family and he is so wrapped up in his job at the Ministry that he doesn't seem to have the time to devote to a girlfriend and/or future wife. However, he may surprise us all and when he does come back to apologize to his parents for his actions, he may already have a wife and a child. Fred and George also seem like the type who would rather run their joke shop and fight in the war than bother with women. Ron is being dense about his love for Hermione and his devotion to Harry and fighting for the cause is also his main focus in his life. As for Ginny, Molly would most likely forbid her from trying to drop out of Hogwarts and abandoning her studies to fight in the war and begin a family. Also, Ginny isn't of age yet, so it isn't ethical for her to be contemplating marriage and a family.
Arthur and Molly are the most likely candidates for bringing a baby into the mix, as they raised their first seven children during a time of war. I also believe that with Arthur working extremely hard and long hours for the Ministry during Voldemort's first reign, that Molly's main source of joy and hope were her children. I believe they helped her see that as long as there are children the world, everything will be all right in the end. As their children are growing up and away from them, Arthur and Molly are feeling the effects of having an empty nest. Molly is most likely lonely most of the time, with no children to take care of and Arthur at the Ministry all day. This time, she doesn't have the daily tasks of raising children to keep her busy and her mind from worrying about Arthur while he's at work. As we know witches and wizards live to well over a hundred years old, Molly and Arthur have at least a hundred years of their life left. With no grandchildren yet and Arthur still working at the Ministry, Molly hardly has anything to do all day. If she and Arthur had another child, there would be hope, love, faith and joy injected into this time of darkness, as well as give her and Arthur a child to take care of while their other children are fighting evil, working, or at school.