Part of the growth of Mormonism is outreach - and a large part is demographic. They have 2.5 kids or more, while most Americans have 1.5.
Around here, the rule is for Mormons to have 4 to 6 children and also adopt 4 more. At the same time, I know people (Christians) who would love to adopt even one child but get the bureaucratic run-around from state agencies, plus from foreign bureaucracies when they try to find a child over there.) How does that work? (I am good terms with the Mormons, but I just recently noticed this pattern for the first time when visiting at an event.)