(FORTUNE Magazine) – Koala Technologies, a California manufacturer that came up with a successful electronic blackboard called KoalaPad, recently introduced an IBM PCjr version of a computer keyboard that looks as if children might have designed it themselves--its latest hit among the learning set. Preschool kids are often captivated by the video kinetics of home computers, only to be turned off by confusing keyboards designed for grownups. Joining forces with the growing Muppet empire (see Managing), Koala developed Muppet Learning Keys. Letters are in alphabetical order, the delete button is in the shape of an eraser, colors are arranged like a watercolor set, and all fit on one piece of plastic that can be wiped clean of the worst grime a child might smear onto it. Priced at $80, Learning Keys also operates with the Apple II, Commodore 64, and Atari 800. About 50,000 have been sold since they were introduced last fall and analysts expect other companies to follow with similar products. The new keyboard could prove helpful to the growing market for instructional software for children. Almost 50 companies generated $180 million in sales during 1984, nearly twice the figure for 1983, according to Talmis, a New York-based market research firm. But using such software requires mastery of a basic keyboard, which is no small feat even for adults. Some companies have produced plastic overlays for keyboards that make the job easier for children --but the software for them is limited and they generally work on only one computer make. ''There's probably nothing on earth you could do to keep kids from getting into computers,'' says Marylyn Rosenblum, vice president of product development for CBS Software. ''Learning Keys just makes it more accessible.''