The children invented a fantastic tale about where they had been all afternoon.

invented 是动词 invent 的过去式。invent 由前缀 in-（表示"进入"）和词根 vent（来自拉丁语 venire，意为"来"）组成，原意是"发现、找到"，后来演变为"发明、创造"的意思。在这里指"编造、虚构"故事。