she already had babies but both parents carried a gene that gave the babies a health problem so husband had a vasectomy so no more kids, but then discovered his wife was desperate for another healthy child, so set about trying to solve this problem.
getting curious about his wife's girls nights out, and fuelled by rumour and guess work he makes too many enquiries too his wife about what goes on, so she gets him invited but he has to do as she asks prior to leaving home.
A weedy old man on the train offers him three wishes. He's the sceptic and a smart ass so he names two sexually charged wishes to shock the old guy. "Granted" he replies. They arrange to meet again in three weeks to hear the third wish. He thinks nothing of it until hours later he discovers that his second wish has come true. He decides to see if his first wish also comes true.