In the Western part of the country, a disturbing pattern is unfolding: children of mothers who fled a fundamentalist polygamous Mormon sect are vanishing — and their families fear it’s part of a radical religious agenda. In the latest case, Elizabeth Roundy of Jefferson County, Idaho, says her two youngest children, 13-year-old Allen Larand Fischer and 15-year-old Rachelle Leray Fischer, disappeared last month while she was at Bible class.