What is the ruling on water or moisture that appears under a closed diaper of a child if it has an unpleasant smell, and what is the ruling on praying on a prayer rug that this water might have touched, and how can dry impurity on a large prayer rug or carpet be purified?

You must dismiss obsessive thoughts and pay no attention to them. Impurity does not transfer from a dry diaper to what it touches. If you doubt the purity of something on the floor or carpet, the default is that it is pure.

If you are certain of impurity on the floor due to a wet diaper or dry impurity meeting a wet surface, then it is purified by pouring water only on the impure spot. It is permissible to follow the opinion of those who consider the earth purified by dryness, to ward off obsessive thoughts.

The default for carpets is purity, and they are not judged impure except with certainty. Their purification is done by pouring water on them.