In reality, the status of a relationship doesn't really have anything to do with having a child, and the risky woohoo mod, by polarbearsims, adds a smidgen more authenticity (and shock) to pregnancy. So far, i have found a mod that comes dang close, but no cigar. There are a couple of woohoo mods available for teen, married and cousins.
Sims 4 Child Woohoo Mod : The Sims 4 Woohoo and Try for Baby Guide.
