Younglings was the general term for a young Jedi in training or a child in general. Anakin Skywalker is ordered to slay them all, in order to wipe the Jedi off the face of the galaxy. Either that, or he cut a hole in the building to let them escape. It isn't clear. He literally just turns on his lightsaber. However, people think he killed them all, as he had a tendency for killing not just the men, but the women and children too.
In one episode of JakeMac's beloved Yoda series, Yoda turns the younglings into Mashed Potatoes.