It happened Tuesday morning when the group went into the Exploratorium.
Kamiya-Lee Luchetti, 5, became the one-millionth person to visit the museum since it reopened on the San Francisco Waterfront last April.
The Exploratorium's executive director greeted the family and handed them a bag of goodies and an annual membership to the museum.
"I love science. And we don't have very much of that at home, but I really like doing things like science," Luchetti said.
Luchetti didn't waste much time trying out the displays.
Reaching 1 million visitors in less than a year is quite an accomplishment for the Exploratorium.
It used to average about 400,000 people a year at the old site.