From The Congressinal Research Service: At the beginning of the 112th Congress, there were 118 Members (21.8% of the total membership) who had served or were serving in the military, 2 fewer than at the end of the 111th Congress, and 8 fewer than in the 110th Congress.35 According to lists compiled by CQ Roll Call, the House has 92 veterans (including 1 female Member, as well as a Delegate); the Senate 26. These Members served in World War II, the Korean War, the Vietnam War, the Persian Gulf War, Afghanistan, Iraq, and Kosovo, as well as during times of peace. Some have served in the Reserves and the National Guard. Three House Members and two Senators are still serving in the Reserves, and three House Members and one Senator are still serving in the National Guard.
As noted above, one Senator is a former Secretary of the Navy.
The number of veterans in the 112th Congress reflects the trend of a steady decline in recent decades in the number of Members who have served in the military. For example, there were 298 veterans (240 Representatives, 58 Senators) in the 96th Congress (1979–1981); and 398 veterans (329 Representatives, 69 Senators) in the 91st Congress (1969–1971).
Another thing to consider when asking about the children of members is the age of the member themselves. “The average age of Members of the 112th Congress, although lower than that of the previous Congress, is among the highest of any Congress in recent U.S. history.6 The average age of Senators at the beginning of the 112th Congress was 62.2 years. This is approximately nine-tenths of a year lower than that of the 111th Congress (63.1 years) but half a year higher than that of Senators in the 110th Congress (61.7 years).”
I couldn’t find anything on personal choice of members to not have children, members who were not able to conceive or mortality stats on children of Congressional members, stats on the personal beliefs of the children of Congress regarding volunteering for US military service, et al.
http://www.senate.gov/reference/resources/pdf/R41647.pdf