Does one become impure by sitting on a mattress that has been stained with a child's urine and then had a small amount of water poured on it, less than two Qullas, while remaining wet from the effect of the poured water?

It is not a condition that the water poured on an impurity be two qullas or more; rather, it is sufficient for it to cover and purify it. If this is done, then the bedding has become pure. Impurity does not transfer from impure bedding to the one sitting on it unless one of them is wet or damp.