They change the last bit of dialogue when it's a dangerous day. I remember Poppy being like "Heyyy, wanna give me your heroic seeeed?", Tristana asks you for a condom for "no reason at all", Sylphy asks you to use a condom unless you want a baby, The Average American Girl is similar, calling kids "lil' Tykes", and the japanese name mommy is aslso like that but dignified.
Sleep in your room a couple of times until they get fertile. Even so i already impregnated the Mommy one outside her fertile window by just having very virile semen, and she's the only one who let you know about the pregnancy (by repeating the same event everytime a new day clocks in until she gets into her Preggo Sprites).