
Plan two rests and one sit-down meal.
Two things make Iwate easy with children, as everywhere in Japan: every station and roadside stop has a proper changing table, and convenience stores sell food a child will actually eat.
Photograph your child that morning, showing what they are wearing, and agree one meeting point as you arrive. If it happens, tell the nearest member of staff or a police box at once. Say Kodomo ga imasen (my child is not here) and show the photograph. Tell someone in the first minute — staff here start looking straight away.