What makes you think Christian’s and others who hold this view expect no child to get pregnant? What makes you think Christian’s and others who hold this view keep their kids ignorant about birth control methods?
Many kids I went to HS with were sexually active and got pregnant and many ended them in abortions. Even my best friend brought his 15 year old girlfriend to NY (one of the two states it was legal) to have an abortion and I know for a fact he had condoms and his girlfriend had free BC pills from planned parenthood. It happens with education, with pills and with condoms.