What is the ruling on praying in clothes that have been soiled by the urine of children, and must they be changed for the prayer to be accepted?

Clothes soiled with urine must be changed or purified, as the purity of one's garment is a condition for the validity of prayer. If someone's garment becomes impure and they cannot find a substitute or enough time to purify it, leading them to miss congregational prayer without any negligence on their part, then there is no sin upon them.