Question: how to get a birth certificate in the sims?
Answer: You first get a Birth Certificate, either by joining Sims giving birth at the GTW Hospital lot (I believe it'll be in one of your Sims' Inventories), or cheat for it in Build Mode by pressing Control+Shift+C, then type "bb. showhiddenobjects" (no quotes), then press Enter, then Escape to close the cheat box.