premise: A childing hiding in a snow fort. hypothesis: The child plays in the snow.
entailment: Building, and hiding in, snow forts is a particular type of winter play.  For the child to have a snow fort to hide in, there must be snow readily available with which to make the fort; as snowfalls generally cover large areas with snow, one deep enough to allow the child to build a snow fort without having to trek great distances to collect snow would leave plenty more snow readily available to play in.