Keeping the home cozy in winter is as easy as snuggling up near the Rais stove or the fluffy pooch.

A Woodchuck-made loft bed anchors Sam's room. The dark green playmat is by Alex Playmats.

Kidroom

Brayden's playroom, located under his lofted bed, is clad in black-and-white foam tiles and a coordinating accent wall.

Benedetta's son's bedroom, which is on the second floor of the villa. The bed is her own design.

Salminen built the bunk beds out of birch, Finland’s most plentiful tree species, for the couple’s children.

This Murphy bunk bed, the Lollipop IN model from Resource Furniture, stows away flush to the wall when not in use.

Leo's new play-space has quickly become Eric's favorite part of the home. "It was one of the most simple projects to build, but the most satisfying to complete because of the look on Leo’s face when he first climbed inside and saw all his toys in HIS space," he notes.

The "Tippy Cup Rain Chain" teaches the children about water conservation.

Visitors scale a series of outdoor staircases that wind their way up the structure. Volume and Studio Terpeluk turned the risers into a teaching moment about energy use and the impact of every day activities.

Mithun designed the tree house so that it would tread lightly on the land. The firm originally considered prefabricating the entire structure offsite but, in the research process, concluded that craning large modules into place would potentially harm the canopy. A combination of a bolted-together prefab structure and site-built wood housing yielded the least intrusive construction option. The Summit Bechtel Reserve is located in West Virginia's coal mining country. The architects looked to the local structures—bridges, mining apparatus, and other industrial buildings—to inform the tree house's design. A 166-ton Cor-Ten steel megastructure supports the 125-foot-tall building. The use of regionally appropriate materials, like steel and black locust wood, was important to the architects.

Now three, Nate occupies coveted corner real estate in a third-floor room with a treetop-level view. “It’s a great space,” Casale says, “although it is the noisiest room in the house because of the street. But by now he’s so used to sleeping through all of the sounds, I don’t think it bothers him.” The brightness of the space is enhanced by an accent wall coated in fire engine–red chalkboard paint (Benjamin Moore Natura flat-finish paint in Vermillion mixed with unsanded grout) that Nate can scribble on—as soon as his parents get around to telling him that it’s allowed. A matching red pendant lamp from the Soho shop Kiosk hangs above a six-foot-tall teepee by Dexton Kids.

Mithun wanted to engage the scouts with all elements of the forest: the floor, the canopy, and a perspective above the tree tops. In one of the viewing rooms, visitors get the feeling of being fully surrounded by leaves.

The structure's mission is to teach visitors about the environment and sustainability. San Francisco–based studio Volume designed the exhibition program, which offers interactive displays about water conservation, energy use, recycling, and more.

1/2 basketball court Architect: James Dixon, Railings: Keuka Studios, inc

In the booming British beach town of Margate, longtime locals Natasha Hart and Oliver Whitmarsh teamed up with newcomer architects RL-a to salvage a 19th-century workers’ lodging. Their son Stan’s bedroom includes a vintage Habitat Skipper bed by Loïck Peyron and a climbing wall designed by Natasha. The plywood finishes are kid-friendly and also affordable.

In a home in Los Angeles, a child's bedroom has been outfitted with custom carpeting and millwork, a reading nook under a staircase, a mini door and window, and a magnetic chalkboard wall.

Mehdi and his wife, Sanae, have six-year-old twins, each with his own bedroom. The early-bird son’s room faces east, while the south room is for the son who likes to sleep in. The tipi was a gift from Mehdi’s father, also an architect.

Chicken under glass? Apolo will settle for eggs for breakfast.

View into the kid's bedroom

Ankory and Carni designed a storage unit under the stairs with a pull-out table and bench where their kids can play and do their homework.

In his room, Finn sits on a Stump stool by Kalon Studios at an oak table from Canvas Home. The flat jute rug is from ABC Carpet & Home; the stainless-steel door hardware is by Emtek.

Awkward sloping ceilings are put to good use in this family apartment known as the Starburst House in Beijing, China. Across from the living lounge, tucked under the mezzanine study, is a child’s playroom. Mountain-shaped wall cushions line the wall, echoing the peaked ceiling.

Finn's street-facing room at the front of the house is enlivened by varying window sizes.

The new structure contains bedrooms for the couple and their sons Elijah and Isaiah.

The long-leaf-pine roof decking was salvaged from the original home and used on the ceiling in the new playroom.

The expanded west end followed the existing layout and incorporated similar wood windows found elsewhere in the home. The children’s bedrooms now have direct access to the light-filled playroom, which opens to the front yard.

A Rafa Kids swing hangs below the loft bed near the large desk designed for playing with Legos.

Paul spreads out his toys on a rug from Pottery Barn.

"Some of my favorite spaces are those that weren't even necessarily planned," says Shahane. "For instance, underneath the stair on the first floor it ended up being a few inches deeper than initially planned because of plumbing requirements. But those inches made a perfect and impromptu alcove for our daughter's drawing table."

“There are floor-to-ceiling windows in almost every room,” says Kaja Taft of her prefab home in Portland. “Light was a big part of why we loved this design.” With so much light comes the need to block it out at times, especially in the children’s rooms. Though the couple invested in solar shades and blackout curtains by Mari Design, “They still get up at 5:30,” Kaja says with a laugh. As in all the bedrooms, the carpet tiles are from Flor.

Lawrence, seven, shows off his toy collection on a vintage Cado wall unit in his bedroom,