CBS will introduce four new shows and break up its Saturday morning powerhouse tandem of “Garfield” and “Teenage Mutant Ninja Turtles” next fall, the web announced at its children’s upfront presentation yesterday.

ABC also announced four original half-hours for its Saturday fall schedule yesterday, but unlike Fox Children’s Network and CBS — which are relying heavily on pre-established products like “Dennis the Menace”– ABC is introducing several original concepts.

CBS is currently No. 1 with kids 2-11 in every half-hour from 8:30-11 a.m. with “Little Mermaid” (Disney), two half-hours of “Garfield” (Film Roman) and two half-hours of “Ninja Turtles” (Wolf Films). But CBS hopes that by hammocking “The All-New Dennis the Menace” (DIC Enterprises) between its established hits at 10 a.m., it will get that show off to a fast start and improve its late-morning ratings by bridging “Turtles” over the 11 o’clock hour.

CBS is looking to the John Hughes theatrical live-action release of “Dennis” this summer to create awareness and anticipation for the cartoon. The net is also introducing a new show at 8 a.m., “Marsupilami” (Disney), and a whole new look from 11:30 a.m.-1 p.m.: “Cadillacs and Dinosaurs” (Nelvana); “Beakman’s World” (Columbia), which moves over from syndication; and, returning from hiatus , “CBS Storybreak” (CBS Entertainment Prods.).

Gone from the web’s ayem sked are “Grimmy,””Back to the Future,””Raw Toonage, ” and “Fievel’s American Tails.”

CBS will again use prime time specials — like “Dr. Seuss’ Cat in the Hat”– as promotional vehicles to help launch the new programs. The web also announced a mid-season series based on a well-established property, “Conan & the Barbarian Kids” (Sunbow Prods.) and that Disney’s “Aladdin”– headed for syndication as part of “The Disney Afternoon”– will debut as a CBS series concurrently in 1994 -95.

Mike Nowacki, VP of children’s sales, told advertisers “(that kids ratings on the networks) has avoided the shrinkage that has plagued the syndication marketplace.”

ABC, meanwhile, will introduce “Cro” (Film Roman and Children’s Television Workshop), an animated series about the Ice Age that tries to teach basic mechanical production, at 8 a.m. In total contrast, the web’s other educational show, “CityKids” (Jim Henson Prods. and CityKids Foundation) airs at 11:30 and uses comedy, dance, animation and Muppets to explore the problems and issues of contemporary urban teen life.

ABC is also debuting two lighter shows –“Sonic the Hedgehog” (DIC Enterprises) featuring the voice of “Family Matters” star JaleelWhite, and “Tales from the Cryptkeeper” (Nelvana), from a creative team including Richard Donner, Walter Hill and Robert Zemeckis (based on HBO’s “Tales from the Crypt”). “Sonic” will air at 9 a.m. and “Tales” at 10 a.m. (Daily Variety, March 22).

ABC returning series are “The Addams Family” (Hanna-Barbara), “Wild West C.O.W.-Boys of Moo Mesa” (King World and Ruby-Spears), “Bugs Bunny and Tweety Show” (Warner Bros.) and “Land of the Lost” (Kroft Pictures). The web also announced a midseason pick-up on “Reboot,” featuring computer animation, to premiere in spring 1994, from Limelight Prods.

Disney’s “Goof Troop””New Adventures of Winnie the Pooh,” and “Darkwing Duck” move from ABC’s network lineup to Disney’s syndicated schedule.

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