Save and consensual sex only! - Would be the savest thing to do.
(Sure you followed what was going on here on itchio regarding adult themed games recently.)
As a dev i would not offer the theme in question at all, exactly bacause of the "age" restrictions you mentioned. If the update would be called "Improved Sex" only that would be perfectly fine and reasonable.
The game has so much things to offer:
Enjoy the food! Indulge! Date multiple characters at multiple locations! Have Girlfriends! Marriage! Differnt Jobs! Sculpt Bodies! Fatness and Fitness! Fun at your sweet home! Have fun at the beach! Watch a movie! Eating competitions! Travel to other towns! Have Save and Consensual sex!
.... the list goes on and on.
Thus: Most ppl could get over not having pregnancy. If someone exclusively follows that specific fetish the game might not be for them.
If added, pregnancy shoud absoluteley be toggleable. Even if enabeld there should be another switch in settings between save sex and try for impregnation.
To be clear: i will not even enable pregnancy for testing purposes. I am not into the theme at all.