Why is the method of cleaning urine differ between baby boys and baby girls under two years old?

Summary

Infant urine must still be cleaned, and scholars agree that urine of a child over two years who eats food is impure and must be washed. For a baby boy under two who consumes only his mother's milk, the Hanafi and Maliki schools make no distinction from a baby girl, while the Shafii and Hanbali schools treat it as light impurity cleansed by sprinkling water. Girl's urine is washed or poured over with water, based on the hadith of Abu Samh. The fatwa stresses that the texts must be accepted, though asking about the wisdom is not wrong, and it cites a modern study finding more bacteria in baby girls' urine.

Written in our own words from the original fatwa — check the source before acting on it.