Dazai and Chuuya were under orders to kidnap a current kid at the adress given from Mori, their boss. They were the mafia, obviously, it wasn't their first time to kidnap someone. They knew the parents were headed off on a business trip. They waited for the babysitter to go out the house, and they barged in. Dazai: "Why would Mori need a kid anyway? He's a mafia boss, he has more armies to need a kid." Chuuya: "Shut it, idiot. We haven't even met the damn kid."