Although they couldn't swim, the two little cubs had quickly figured out one survival tactic. If they thrashed their paws around fast enough, they would stay above the waterline - even if they weren't going anywhere. That bought them some time, but didn't buy them much hope.
They couldn't see or hear their mother anymore. They also couldn't see their way to the island. As far as they were concerned, she'd vanished without a trace. They were helpless and hopeless.