Does touching an uncircumcised child invalidate the prayer of someone who is praying?

The basic principle is that children's clothes and bodies are pure, until their impurity is established with certainty, based on the saying of Al-Hafiz Ibn Hajar: "Children's clothes and bodies are considered pure until impurity becomes evident." Consequently, if a child touches someone during their prayer, their prayer is valid, regardless of whether the child is circumcised or not.