Children's museums in America are delivering a report card to be envied.

Since 1990, an estimated 100 youth museums have opened, with at least 80 more in the planning phase. There are now 215 such institutions in the United States focusing on a variety of themes and subjects, although many are heavily oriented toward science. In 1975 there were only 38 children's
museums, a field that has existed since the opening of the Brooklyn Children's Museum in 1899.

With the availability of these new facilities, attendance has skyrocketed.In 1991, a total of 8 million people visited children's museums in this country-fewer than the number who visited the National Air and Space
Museum; last year, 33 million people went through their doors.

This cheerful picture is part of a comprehensive look at children's museums that will be released this week by the Association of Youth Museums during its annual conference in St. Louis.

The growth can be traced to the rising number of children in the country (almost 80 million Americans are under 20), the push to foster learning from a variety of approaches, the increasing popularity of museums in general and the encouragement of public and private planners who view these repositories as energetic and safe attractions in downtown development.

"Children's museums are the fastest-growing cultural institution in the world," says Janet Rice Elman, the association's executive director. "That trend will continue as we see more communities wanting to start up a
children's museum to enrich civic and family life."

Developers are attracted by the popularity of children's museums, especially as dormant downtown areas are redone. The association says that 73 percent of children's museums are in urban areas.

"The appeal is to bring families into downtown. That is something many cities lost. They became work, ceremonial and entertainment places for adults," says Lou Casagrande, the president of the association a!
nd of the 90-year-old Children's Museum in Boston. He says children's museums function as town squares where "you feel at the center of your community."

These museums also bring in revenue because the children are usually accompanied by adults. The average expenditure per visitor, according to the association, is $9.26, an increase of $1 since 1999.

The association reports that 54 children's museums are flagships for revitalization projects in cities that range from Wichita, Kan., to Green Bay, Wis. Some have the "town square" viewpoint built into their architecture. Port Discovery near the Inner Harbor in Baltimore, for example, has a Main Street arcade right inside the front door.

With growth has come competition to build better, more intricate, facilities. The association reports that more than 25 percent of its 200 members are mounting capital campaigns for new or expanded facilities. Florida is a hotbed for this sort of fundraising, including a $15 million campaign in Miami and a $37 million one in Tampa. Six different efforts are underway in New York, including a $27 million campaign for the lauded Brooklyn
museum. A group in Tuscaloosa, Ala., is trying to raise $1.5 million for a facility.

In St. Louis, the Magic House raised $4.2 million for a renovation that doubled the size of its facility and now attracts 400,000 visitors a year.

In Washington, the Capital Children's Museum, located on Capitol Hill, attracted 200,000 visitors last year, up from 180,000 in 1999. That bests the average annual attendance nationally, which the association estimates
was 171,732 last year.