Passport or Passport card is all the adults need, and a birth certificate for anyone under 16.
Also, if you ever try to cross the border without both parents, I'd suggest a notarized permission slip from the parent not with (not sure if its necessary, but I can tell you from previous experience its helpful. And I can also tell you not to cross the border as a group and put the guys in one vehicle and the girls & kids in another, that really confuses them)
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