The children spotted several sticklebacks with spiny backs in the creek.

sticklebacks 是 stickleback 的复数形式，stickleback 由 stickle（刺）和 back（背部）组成，字面意思是"背部带刺的鱼"，指一种小型淡水鱼，中文称为"刺鱼"或"棘鱼"。