Well, there's a lot of variance in definitions — it used to be that young women of 13 or 14 were married off (many cultures have a special coming of age celebration of a girl's first period, the biological signal that she'd of child-bearing age), nowadays "children" can be up to 26. So, using that definition, there's a vast number of people in America's history who married children.
(This is, I believe, the result of having so many arbitrary ages — instead of a single debarkation-point like 18 being the age of majority and sticking with that. [Well, I would be fine with three 'classes' insofar as age goes: 0..12, 13..17, 18+])
Jerry Lee Lewis and his third wife Myra Gail. Jerry age 22 Myra age 13.