Answered by Sidi Mostafa Azzam
Is it permissible to carry a child who might have a wet diaper in prayer?
Says The Immaculate Raiment, “The following must be free of unexcused filth: your body, what you are supporting, and anything touching or connected to them.” So carrying a child that definitely has filth in its diaper is invalid and impermissible, since you are supporting filth. That is if the filth is established. As for if it is merely possible, it is assumed to be pure. The presumption on everything is purity, and that presumption is not overruled by uncertainty about the occurrence of filth, since certainty is not overruled by uncertainty. So, yes, it is permissible to carry a child who might have a wet diaper in prayer (provided it does not interfere with any of the other essentials of the prayer, such as avoiding excessive movement).