An unmarried child under twenty-one at the relevant date can be included, and the child-status protection rules may preserve that eligibility during processing. A married child cannot be a derivative.
Age and marital status are tested by rule, not by intention
EB-5 derivatives are the investor's spouse and unmarried children under twenty-one. A child who is twenty at filing is within the rule, and the Child Status Protection Act may freeze or subtract processing time so that the child does not age out while the petition is pending, provided the child seeks to acquire status within the required period after a visa becomes available. Whether that protection holds depends on the dates, so the family should calculate it before filing rather than assume it.
A child who marries before immigrating loses derivative eligibility entirely, and no later filing restores it as a derivative. Derivatives who immigrate with the investor receive the same conditional residence and are included in the later removal of conditions. Plan the family list now, and if a child is close to the limit, treat the filing date as time-sensitive.