If Anakin didn’t kill the Younglings in Episode III, Yoda probably would have done the job for him through sheer incompetence.  I mean seriously, who does give children lethal weapons?  Force or no Force guiding them, kids would start play fighting with a lightsaber the second you gave it to them.  Although I guess there are such things as Training Lightsabers, I’m just going to assume this happened before those were put into use.