Not as described. Conditional permanent residents, including the child as a derivative, are expected to reside in the United States, and long absences can be treated as abandonment. EB-5 gives the whole family residence, not a stored option for one child.
Residence cannot be held in reserve
The family's plan reflects a widespread misunderstanding. The immigrant visa admits each of them as a conditional permanent resident, which is a status defined by living in the United States. Absences of more than a year generally require a re-entry permit, and even shorter absences invite questions if the family's home, employment and schooling remain in Canada.
A pattern of brief entries to preserve a card is the kind of fact that leads to a determination that residence was never established. The child's status is derivative of the parents', so it cannot be kept alive if theirs is not. There are also tax consequences: permanent residents are taxed by the United States on worldwide income from the day of admission, whatever the number of days spent there.
If the genuine intention is to give the child a future option, the honest sequence is to delay the investment until the family will actually move, or to plan a move that coincides with the visa. A child who turns twenty-one before the immigrant visa is issued may lose derivative eligibility, subject to the statutory age-protection calculation, so a delay should be timed with that in mind.