Maybe they can serve as spokes-critters for a Save Our Wetlands campaign.

After all, they're pretty irresistible, these amphibians -- and other fauna -- who frolic through the Round House Theatre's "A Year With Frog and Toad." Robert and Willie Reale's family-friendly musical, which ran briefly on Broadway in 2003, presents a marshy world of sweetness and light -- a place where friendships are indissoluble and days brim with such simple pleasures as flying kites and eating cookies. Pessimism and archness are endangered species, and in the wrong hands the aesthetic could well be too wholesome by half.

Fortunately the top-tier performers in this Round House production fling themselves into their roles with such expressiveness and gusto -- supported by Nick Olcott's witty direction and a handsome, kaleidoscopic set -- that even hardened cynics might start to feel like Dr. Dolittle.

Based on the children's books by Arnold Lobel, the musical chronicles the peaceable activities of two buddies: the cheerful, athletic Frog and the slightly insecure Toad, who live in harmony with assorted birds, moles, squirrels and a very obnoxious Turtle. Robert Reale's light, jazzy score, harking back to tunes of the 1930s and '40s, buoys Willie Reale's wide-eyed lyrics, giving us such numbers as the ragtime-inflected "Getta Loada Toad" ("Two things you cannot dispute / Bamboo comes from a bamboo shoot / And Toad looks funny in a bathing suit") and the snappy ditty "Cookies" ("Eating cookies, eating cookies / We're so happy eating cookies").

If anyone can lend brio to this kind of amiable naivete, it's the Round House cast, headed by Will Gartshore and Steve Tipton. Gartshore (recently in Signature Theatre's "Urinetown") gives us a Frog with dazzling, old-fashioned charisma -- a veritable Gene Kelly of the lily pads. Forget all that Kermit stuff about it not being easy being green. Gartshore's Frog is blithe and radiant from the moment he springs out of his hibernal bed, tears off his nightcap and rushes over to the neighboring cottage to wake Toad for the spring.

With his hyper-animated face percolating with Toad-like emotions -- disgruntlement, balefulness, perplexity -- Tipton makes a droll counterweight to the debonair Frog, the difference in temperaments adding great sweetness to the musical's portrait of friendship.

Providing terrific supporting turns are the other three cast members: Erin Driscoll, Sherri L. Edelen and Bobby Smith, who impersonate various quirky varmints and soft-shoe around as a chorus of snarky birds. Smith, in particular, does a show-stealing cameo as the cowboy-style Snail, shuffling along determinedly in a ten-gallon hat ("I put the go in escargot").

All the performances profit from costume designer Rosemary Pardee's clever anthropomorphic costumes. The birds show up in fawn-colored suits and feathered hats, looking rather like traveling salesmen. Frog and Toad romp about in preppy sweaters and jackets with tweed caps and sneakers. Turtle sports a pith helmet.

The understated eccentricity of the costumes suits the pleasant, low-key vaudeville choreography by Michael J. Bobbitt. Considerately de-leafing each other's lawns, Frog and Toad caper with their rakes a la Fred Astaire. The birds tap-dance and sashay through some variations on the Charleston. And in a surprise cabaret number, "I'm Coming Out of My Shell," Snail tears off his lumberjack shirt, emerges in a spangled blouse and shimmers through a few Bob Fosse-style moves with a bowler hat.

Jos. B. Musumeci Jr.'s adorable set bolsters the mood of genial innocence. Blue-green plants and an ornamental dragonfly, flat and paneled like coloring-book images, arch over Frog and Toad's tiny cottages, which spin to reveal cozy interiors. A pondlike circle of reeds cuts a silhouette against the pale backdrop, which lighting designers Daniel MacLean Wagner and Harold F. Burgess II frequently saturate with Easter egg colors.

Human adults might not want to dally too long in this idyllic animal kingdom (you'd start to long for danger and cynicism, or at least some wisecracking Disney characters). But at under two hours, it's bright and beautiful for creatures great and small.

A Year With Frog and Toad, music by Robert Reale, book and lyrics by Willie Reale, based on the books by Arnold Lobel. Directed by Nick Olcott; music direction, Jay Crowder; costumes, Rosemary Pardee; sound, Tony Angelini. Approximately 1 hour 45 minutes. Through Dec. 18 at the Round House Theatre Bethesda, 4545 East-West Highway. Call 240-644-1100 or visit www.roundhousetheatre.org.

Bobby Smith's quirky Snail livens up Round House's "A Year With Frog and Toad."Will Gartshore's Frog (with Sherri Edelen's Turtle) is all charisma -- a veritable Gene Kelly of the lily pads.