Bumping out a wall for a built-in twin bed creates a cozy sleep alcove.

Red twin fitted jersey sheet, $25 at Warm Biscuit Bedding Company. Similar pillow: Alpaca textured pillow cover in Natural/White, $39 at West Elm. Similar artwork: Two-Humped Camel giclee print, $50 at AllPosters.com.

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Bring the thrill of camping indoors with wildlife elements and a play teepee.

Similar table: Sansad children’s table, $50 at Ikea. Great Plains Child Indian Teepee, $89 at Fantasy Toyland. Flat Roman fabric shade in Catalina Stripe/Pear, $228 at Smith & Noble. Inflatable deer head, $20 at Prank Place.

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For furnishings that he won’t outgrow, choose pieces with traditional lines, like a classic wing chair and a mahogany spool bed.

Similar bed: Jenny Lind full bed, $599 at Land of Nod. Orleans twin quilt in Blue Sky, $128 at Garnet Hill. Similar chair: Dickson chair at CR Laine. Similar artwork: Bean Sprout Silhouette Safari wall art, $35 for set of three at Target. Similar bed skirt: Navy flannel twin skirt, $65 at Warm Biscuit Bedding Company. Rens sheepskin, $25 at Ikea.

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Pairing farmhouse-style furnishings with a white-toned blue wall color creates a homey, cheerful room.

Custom pinch-pleat curtains in Vintage Cowboy Stampede, $295 at Warm Biscuit Bedding Company. Similar dresser: Kendall drawer chest, $849 at Pottery Barn Kids. Similar bed: Fresh Scallops white twin bed, $599 at Land of Nod. White capital letters, $10 each at Pottery Barn Kids.

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Whimsical elements, like soaring tree silhouettes and trompe l’oeil closet doors, make an imaginative room that’s ideal for dramatic play.

Feelin’ Groovy carpet tiles in Cobalt, $12 each at Flor. Fatboy Junior beanbag chair, $149 at Design Public.

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Painting wide horizontal stripes in cool shades of blue creates a calm background for graphic decor.

’50s Birdcage twin cuvet cover, $58 at Urban Outfitters. Similar rug: Kite kilim rug, $229 at West Elm. Similar artwork: Don Quixote poster, $16 at AllPosters.com. Flensted “Flowing Rhythm” mobile in Red, $54 at 2Modern.

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A vibrantly patterned bed and bright green walls create a fresh, high-contrast look.

Feel the Energy (417) paint at Benjamin Moore. Similar bed: Skyline Furniture Nicole upholstered twin bed, $480 at National Furniture Supply. Similar table and chairs: Children Crayon Pencil-Style Table and Two Chairs Set, $50 at Amazon.com. Similar artwork: Spaniel Hunting Dogs print, $13 at Art.com.

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Small patterns, like checks and ticking stripes, make for a crisp and tidy room.

Similar wallpaper: Waverly Canton Stripe, $19.20 at Wallpaper Factory Outlet. Twin Blue Grid comforter cover, $69 at Land of Nod.

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Take advantage of architectural details, like chair rail and baseboard, and paint each a different kid-friendly hue.

Similar blanket: Sheep Children’s Eco chenille blanket in Blue, $120 at Fjorn Scandinavian. Similar stool: Colby medium bar stool, $99 at Pottery Barn.

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Bright white, honey-toned wood and deep navy provide a natural backdrop for a nautical-themed room.

Similar bed: Walden twin bed in Honey, $799 at Land of Nod. Similar rug: Diamond Denim/White indoor/outdoor rug, $134 at Dash & Albert Rug Company. Similar artwork: Two Fifes: Tuiga and Moonbeam III print, $25 at Art.com. Similar pillow sham: Navy Color Frame sham, $58 at Serena & Lily. Similar lamp: Harbor Tugboat lamp, $99 at Yessy.

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A bed with a slide makes the transition from a sleeping space to a play space.

Similar bed: Play Fort low loft bed with slide by Maxtrix Kids, $1059 at Sweet Retreat Kids. Similar shade: Flat Roman shade in DwellStudio’s Dots Chocolate, $230 at The Shade Store. Wild Kingdom wall art, $99 at Land of Nod.

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Blue and white sponge-painted walls create a serene, sleep-friendly room.

Similar bed: Sloane twin bed in Vintage White, $799 at Restoration Hardware Baby & Child. Similar rug: Dove Gobi Frame rug, $349 at Serena & Lily.

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A slightly lofted bed provides additional toy storage without being too high for little ones.

Similar bed: Low loft bed at Maxtrix Kids Furniture. Beat Our Chest toy chest, $199 at Land of Nod.

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A small room feels grand with a tall, upholstered bed and oversized framed art.

Similar bed: Stanley Young America Mix & Match Antiquity Low Post Panel twin bed in Piano Key White, $979 at Layla Grayce. International Signal flags, $20 each at Flags Georgia. Similar artwork: Dudley the Dog Print, $12 at Art.com.

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