Flash back to when my oldest nephew was given "free agency" to choose, to become a future missionary at the age of 3...

Well there's your problem. You don't have Free Agency. You have Moral Agency, which is defined as obeying the "brethren" no matter what. The thinking has been done, as they tell you.

"We don't do infant baptisms because we believe that people should have the agency to make such an eternally-important decision on their own.

"... Anyway, want to come to little Timmy's baptism? He just turned 8 years old and has decided to promise that he will commit the entire rest of his life to the Church! I'm so glad he's finally old enough to make that choice on his own!"