They're basically wearing swim floaties on their feet.

它们相当于在腿上穿着游泳漂浮物。

And stay in the shallow area. I don’t want to see you go any farther than that sandbar! It’s too deep out there and we didn’t bring your floaties.

待在浅水处，你们最远不要超过那个沙洲。那里太深了，而且我们没将你们的救生圈带来。