The 40-year-old actor called an emergency meeting with wife Jennifer Garner - with who he has Violet, six, Seraphina, three, and six-month-old Samuel - after he learned his spouse had taught the kids some slang terms for male genitalia.
Jennifer recalled: "The girls help a lot with diaper changes. At bedtime they clean their rooms and whatever and one day Ben came in and was like, 'OK guys, come on, there's a lot of junk here' and Sera goes, 'That's what mom says'. So he was like, 'What do you mean?' and she said 'You're the one with junk dad - your penis!'
"He was like, 'Can I see you in the kitchen?' He was like, 'Are you teaching our children to say junk?' And I said, 'How many times a day can you say penis? You've got to call it something!' "
After having two daughters, Jennifer admits it was initially strange getting used to the fact she now had a son.
She told TV talk show host Jimmy Kimmel: "He's doing great, we're used to it now; there's another one and he's a boy.
"Every time you change diapers the first few weeks it's like 'Oh right, you're a boy, there's something else going on, wasn't expecting that.' "