Just make the game without greyscale. If someone complains, then meh.
I understand children and death are a sensitive combination, but nowadays everything is a sensitive topic, so censoring for the sake of censoring seems sad.
If you finish and upload the game with tags such as "gore", "blood" and "children" then someone complaining either didn't read your tags/disclaimers or just wants to whine.
Having children in a gorey enviroment I think makes the player more protective of the character, so the more visible blood, the more the player is inclined to protect there little muffin from the boogie man.
Of course, greyscale is entirely your own option.
IF worst comes to worst, why not do both?
Have the player choose at the start, censor or not. If they choos censor, have it turn on a switch.
Everytime a "grey" event is happening, have it check if switch "censorship" is on. If the switch is ON, turn the screen grey. If the switch is OFF, play the scene normally?
Seems like a rather easy set up if you really want to avoid a backlash later.