Actually the USA is about the only place in the world where large numbers of Christians circumcise infants. In Europe, Gentiles do not (and never have) circumcised. One reason why identifying Jewish men 70+ years ago there was very easy.
I do not know what Muslim practice is, does anyone know?
Seems to vary with Muslims. I read that some Hadiths cite circumcision on the seventh day after birth (which is one day earlier than Jews), and some at age 14 (most likely derived from Ishmael, who was circumcised at age 13).
Something to do with also being children of Abraham...