WASHINGTON, July 4 -- For every American child born in the last eighteen months, the federal government now holds a $1,000 stake in their financial future. What the markets do with it over the next two decades will determine whether that seed investment compounds into real wealth or becomes a footnote to a ceremony.

President Trump formalized the launch Friday morning by simultaneously ringing the New York Stock Exchange and Nasdaq opening bells from the Oval Office, a choreographed assertion of presidential market authority the administration had carefully saved for Independence Day. By early afternoon, the administration said, six million families had enrolled their children.

The program, formally known as the 530A account, is adminis...