As Jewish kids who grew up in New York City six decades ago, Jack and Shirley Silver have fond memories of their summers in private Jewish camps. The camps the couple attended, both defunct now, offered Shabbat services and perfunctory Jewish content, but stressed typical camping activities like swimming and arts-and-crafts.

The Silvers, who live in Manhattan’s Columbus Circle neighborhood, want today’s Jewish campers to spend their summers in more-intensive Jewish camping environments. To make that happen, the Silvers last week made a $20 million legacy donation to UJA-Federation of New York’s network of summer camps.

The donation is the largest ever made to the philanthropy’s Henry Kaufmann Campgrounds (HKC). It will support the new Jewish Day Camp Centennial Signature Initiative and is the latest sign of the increased attention that Jewish camping has received in recent years from the Jewish community.

Surveys consistently show that Jewish camps, a focus of informal Jewish education, rank among the strongest builders of Jewish identity and observance.

In the last few years, major financial support for various Jewish camping programs has come from such sources as the Harold Grinspoon Foundation’s JCamp 180 initiative, the Ruderman Family Foundation, the Avi Chai Foundation and the Jim Joseph Foundation.

UJA-Federation CEO Eric Goldstein called the Silvers’ “groundbreaking” gift “an exceptional show of support for the fundamental importance of Jewish day camping.”

Jewish camps have “always been an important portal for Jewish engagement. In today’s world of more choice and a more disparate Jewish community, Jewish camping is increasing in importance,” said Jeff Schoenfeld, president of UJA-Federation. He said the Silvers’ donation will be used to upgrade the facilities and infrastructure at the HKC 12 day camps on 505 acres of land on Long Island, Staten Island and Rockland County. The camps, part of the largest Jewish day camp system in the country, are run by 15 JCCs and Ys in the Greater New York area, and the Sunrise Association, which provides free camp for children with cancer and their siblings.

The camps were built in the 1950s. “What exists today are facilities that are not competitive with other camps,” said Jack Silver, founder of New York-based SIAR Capital. His wife is a former social studies teacher.

Jewish camps “teach Jewish values, and they do a very good job at it,” he said. “They teach Jewish values every day — on the bus, in free time.”

“They reach kids at a very impressionable age,” he continued. “Camp is usually a wholly positive experience with rich content … both fun and meaningful.” Schoenfeld said the physical improvements at the HKC camps over the next three years will allow an increase of 20 percent of the 6,000 campers who now take part in the UJA-Federation camping network.

Some 200,000 Jewish children this year attended more than 150 overnight Jewish day camps and 130 day camps in the U.S., a steady growth over the decades, said a spokesman for the Foundation for Jewish Camp.

The country’s first overnight Jewish camp was founded here in 1893; many followed in the 20th century, largely offering a “fresh air,” bucolic escape from the steaming city streets. They were designed to “Americanize” the children of Eastern European immigrants; by the 1950s, many of the camps added strengthened Jewish educational and cultural programming.

“We enjoyed camp,” Jack Silver said of his and his wife’s youthful summer memories. Their gift, he said, will allow future Jewish campers to develop similar memories in a stronger Jewish setting, “much deeper than we experienced.”