Children going to camp this summer can be within three feet of peers in the same-group settings, but they must wear masks at all times, federal health officials say. The only times children should remove their masks is when they are swimming, napping, eating or drinking; they should be spaced far apart for these activities, positioned head to toe for naps and seated at least six feet apart for meals, snacks and water breaks.

The Centers for Disease Control and Prevention issued the anticipated updated guidance for summer camp operators this weekend, just weeks before many camps resume operations in mid-May. Many parents have been eager to find camps for their children, who had spent months indoors in remote learning classes during the pandemic.

A theme that runs throughout the updated guidance is the emphasis on conducting as many activities as possible outdoors, where the risk of infection in considered much lower than indoors. When activities must be brought indoors, spaces should be well-ventilated and windows should be kept open (windows should also be open on camp buses and vans), the C.D.C. said.

The guidance urges children not to share toys, books or games. Each camper should have a labeled cubby for their belongings, and nap mats should be assigned to individual children, and sanitized before and after use.

Some activities should still be avoided altogether, including close-contact or indoor sports, and large gatherings or assemblies. Singing, chanting, shouting or playing instruments are recommended for outdoors.

Wearing a mask is a critical piece of the prevention effort, even as federal health officials are weighing whether to lessen that restriction for the outdoors especially among people who are fully vaccinated.

“All people in camp facilities should wear masks at all times, with exceptions for certain people, or for certain settings or activities, such as while eating and drinking or swimming,” the guidance states in the only sentence emphasized in bold font in the 14-page advisory.

Federal health officials also issued rules for overnight camps, saying eligible staff, volunteers, campers and family members should be fully vaccinated two weeks before traveling to camps, while those who are not vaccinated should self-quarantine for two weeks before arriving at camp. Those who are not fully vaccinated should also provide proof of a negative test for the virus, taken one to three days before arriving at the camp.

Campers and staff members should be screened for Covid symptoms upon arrival at camps, and screening tests should be conducted if there is substantial community transmission in the area. Daily symptom checks should also be carried out to monitor for possible illness, the advice says.

Anyone working at a camp who is 16 or older is “strongly encouraged” to get vaccinated “as soon as the opportunity is available,” health officials said.

But immunized individuals must still wear masks around children, who are not eligible for vaccination yet, and stay six feet away from them. Children should also stay six feet away from children in other groups.