Both the premise and accusation are incorrect.
Christians need not produce children
In Orthodox Judaism, the first mitzvah is to "be fruitful and multiply." Christians are subject to the Spirit of Torah, but not the letter of it. Traditionally, the Church has in fact recognized this and never ordained that Christians must have children. In fact, they went so far as to demand that every priest, monk, and nun be celibate and not have children. Only recently (post-Puritan?) have some Christians lost their value of celibacy. Even now, the Church does not demand children; no Christian is denied membership to a church being sterile, infertile, celibate, or just choosing with their spouse not to have children. It's clear hypocrisy against trans people, lesbians, gays, and whomever may fit.
Most trans people do have children
I've met very few childless trans adults and no young trans people that don't anticipate raising children. Any trans person can have chilldren. All cross dressers and drag queens marry people opposite their birth sex and almost all gender queer people do as well. For gender queer people who alter their body to prohibit bearing children, artificial insemination makes biologial children possible. Adoption is alwasy an option as well.
Many transexuals have transitioned later in life, after they've had children. Those who don't, many males freeze their sperm for later artifical insemination. A post-op FTM on hormones can give birth; they just requires a cesarian birth. There are potential risks when doing this, so some females choose not to alter their bodies to risk losing fertility or will have children first and then transition. Adoption is a further option as well.
For the concept that not having children proves a person has not changed sex,see Objection: Sex Never Changes