The Creepy, Horrifying World of Family Relations

With all due respect, it is only "grooming" if you make it that way. Those two Sims do have the possibility of romantic interactions, but you, the player, controls what happens.

Assuming that this isn't flamebait and you are genuinely bothered by the fact that two pixel people may be romantic in a simulation, I'd suggest cheating to give one the unflirty trait. Otherwise, customizable options or mechanics would be nice, but there is no "grooming" mechanic in 4 and there was never meant to be.