premise: Two children play on a barrel turned swing. hypothesis: Some people are swimming in a lake.
contradiction: The statement that two children play on a barrel turned swing does not lead in any way to the statement that some people are swimming in a lake; based on the information provided, there is no indication that the swing is by a lake or that there are other people around, much less swimming.  The swing could be absolutely anywhere in the world, in any type of terrain.