McCain didn't talk about his children very much throughout his career for their own privacy, especially after attacks on Bridget during the 2000 presidential primaries (via The New York Times). Eventually, his wife and children started spending more time in the spotlight when McCain ran for president against Barack Obama in 2008.
"It's intentional," McCain told The New York Times during the campaign. "I just feel it's inappropriate for us to mention our children. I don't want people to feel that, it's just, I'd like them to have their own lives. I wouldn't want to seem like I'm trying to gain some kind of advantage. I just feel that it's a private thing."
At the time, Meghan became the outspoken one and even joined McCain's presidential campaign, according to The New York Times. However, Jack and James McCain were busy following in their famous father's footsteps. John McCain was a military man first, and while he served in the Navy in Vietnam, he became a prisoner of war (POW) from 1967 to 1973. He became a member of the House and then a Senator from Arizona after his release (via Biography).
