Marshfield Kids at Play, the group that built the playground with a mix of public and private funds, always planned to build a pavilion, according to the group’s president, Elizabeth Zimmer. But they didn’t have the money right away. The pavilion costs between $40,000 and $50,000, she said, because it must be capable of withstanding strong winds. It will resemble the playground, made of wood with a green roof, built on a water-permeable rubber surface.

This summer, they have tried to get out into the community again, and that means doing something to honor Emerson and help other families. They’ve started the Emerson Lily Hitchcock Memorial Foundation, through which the family is raising money for SUDC research and local projects that benefit children. Their first goal is to fund a picnic pavilion at the new Marshfield playground near Ventress Memorial Library.

The couple can barely talk about what happened. Normally social people, they’ve kept to themselves for the last 16 months. Scott does a lot of running and biking - things he always did, but now they feel like an emotional release.

Danielle put Emerson in her crib for an afternoon nap, and less than two hours later, the little girl had died.

Emerson had never had a seizure. The day she died, March 1, 2010, everything seemed normal. Scott, a database administrator for the financial services company Computershare, was working from home in Marshfield. Danielle was home, too. A lawyer, she worked part time while taking care of three daughters and managing another pregnancy.

About a third of the cases occur in children who have had a seizure or have a history of one or more fever-induced seizures (called febrile seizures) in the child or a family member, according to Henry F. Krous, a physician and director of the San Diego SIDS/SUDC Research Project. But the majority of cases have no known link, making them impossible to predict. SUDC is a diagnosis of exclusion, which means the death cannot be attributed to any known cause.

Had Emerson been under a year old, her death might have been classified as sudden infant death syndrome, or SIDS, which most parents are acquainted with trying to prevent. But starting at age 1, unexplained death is classified differently, as “sudden unexplained death in childhood,’’ or SUDC, and researchers believe the origins of this little-known syndrome are very different.

Yet no amount of worry can prevent everything or explain the unexplained. On a Monday afternoon last year, when Scott went to wake 2-year-old Emerson from a nap, he found her dead, lying peacefully in her crib.

MARSHFIELD - Scott and Danielle Hitchcock did everything they could to protect their daughters from illness and accidents. They worried about all the things careful parents of young children worry about.

Families like to have birthday parties at the playground, she said, but the area needs more shade, and there’s no room for large shade trees to provide a natural canopy. Marshfield Kids at Play has less than $10,000 to put toward the pavilion. The group is planning a road race in the fall to raise more funds, and they hope the Hitchcocks’ fund-raising will cover the balance.

Toward that end, the Hitchcocks’ first two events take place this month. Scott will swim, bike, and run in the New York City Triathlon this Sunday, and the foundadtion is hosting a Boston Harbor sunset cruise Aug. 19, featuring hors d’oevres, dancing, and raffles.

Scott said he was lucky to get a spot in the triathlon, where most participants must have their names drawn by lottery. He e-mailed John Korff, owner and organizer of the race, in hopes of getting one of the spots reserved for people raising money for charity, but Scott didn’t expect to get a slot until 2012.

Korff read his e-mail. They connected by phone, and he listened to the Hitchcocks’ story. “I had one of those ‘Oh, my God’ moments,’’ Korff said. Scott was in - not for 2012, but for this summer.

He has had little time to raise money for the race, especially with the family still grieving. But the Hitchcocks are forging ahead, even though they don’t always feel ready to interact with the public. In many ways, Scott said, the cruise will be harder than the grueling triathlon because of the need to interact with other people.

The cruise, however, is likely to raise more money - hopefully about $20,000 including the silent auction, Danielle said. About half of the 500 tickets - available at www.emerson-lily.org or 781-834-7003 - have been sold for the catered event, which runs from 7:30 to 10:30 p.m. Tickets cost $65 and the boat will leave from Marina Bay in Quincy, rain or shine.

Danielle, too, has difficulty going out in public. She wears a black rubber bracelet with the words “in mourning,’’ so when she goes out, she can express that the family is still grieving, even though she gave birth to a baby 10 months ago. “Having had a baby, people sometimes think everything’s fine now, and we’re back to having three girls,’’ she said.

But Emerson is still their daughter, and their new baby makes four, not three.

“Unfortunately, their story mirrors so many of our other families,’’ said Laura Crandall, a cofounder of the Sudden Unexplained Death in Childhood Program, part of the New Jersey-based CJ Foundation for SIDS.

After Crandall’s own daughter died in 1997, it was hard to find any information about unexplained death in children over 1 year old. She met Krous at a conference, and they have worked cooperatively ever since. The CJ Foundation for SIDS funds Krous’s research in San Diego, where he also teaches pathology and pediatrics at the University of California San Diego School of Medicine.

Sudden death at age 1 or older is about 50 times rarer than SIDS. Whereas about one in 2,000 infants dies of SIDS, only one child in 100,000 dies a sudden, unexpected death after reaching age 1. Among those, between two-thirds and three-quarters remain unexplained after physicians rule out other causes, according to Krous.

Although his research includes children up to about 15 years old, the vast majority of cases involve children ages 1 to 4. As with SIDS, the children die primarily during sleep, and more boys are affected than girls. But the similarities stop there, said Krous. Research has shown subtle abnormalities in the brains of SUDC children that could predispose them to have seizures in response to a fever, virus, or mild head trauma, he said. The same abnormalities have generally not been found in children who died of SIDS.

Krous has hope that the science of SUDC will continue to advance rapidly. Just a decade ago, he began collecting cases for research, and his first paper on the subject was published in 2004.

The ultimate goal, of course, is prevention. Although much remains unknown about what causes these deaths, Krous recommends that if a toddler has a fever, especially if the family has a history of febrile seizures, parents should take the child to a doctor and seek treatment rather than waiting for the fever to go away.

Jennette Barnes can be reached at jennettebarnes@yahoo.com.

© Copyright 2011 Globe Newspaper Company.