Using a child to make a political statement is wrong.

The Catholic school is a private institution. In that private institution the child will be taught that homosexuality is a sin. It will teach that homosexual couples cannot be married.

Based on that fact alone, I cannot fathom why a homosexual couple would want to send their child to a school where that would be taught.

I do not see how a child could reconcile seeing: two good, loving same sex parents with the concept that they are sinners.