Is doubt about a child's thigh being splattered with urine drops a cause for caution, and is this caution considered a form of scrupulosity (waswasa)?

It is not correct to keep a boy away for fear of impurity, because the default state of his body is purity until impurity is established with certainty. And children walking on the ground does not necessitate its impurity, because doubt does not remove certainty. It has been prohibited to cast doubt on such matters, because doubt develops into obsessive whispering (waswas). Evidence for this is the story of Omar ibn al-Khattab with the owner of the basin, and the saying of the Prophet, peace and blessings be upon him, concerning the man who doubts that something has exited him during prayer, and he commanded him not to leave until he hears a sound or finds a smell, as proof of building upon the default state, which is purity. One must beware of obsessive whisperings and treat them by ignoring them.