The chart masters at Billboard magazine have completed their rankings of the best-selling and top-renting videocassettes of 1990, and their findings confirm two of the truths underscored for the entertainment industries this year: the unprecedented importance of young audiences for both screen entertainment and music, and moviegoers' overriding preference -- despite filmmakers' predilection for big-budget bang-'em-up spectacles -- for comedies that make them laugh and feel good.

Children's tapes dominated the list of best-selling cassettes, occupying six of the top 10 slots. Disney's "Bambi," released in late 1989, led off, followed by "The Little Mermaid" at No. 3, the 50th anniversary edition of "The Wizard of Oz" (No. 5), "Honey, I Shrunk the Kids" (No. 7), "The Land Before Time" (No. 8) and the "Cowabunga, Shredhead" episode of the "Teenage Mutant Ninja Turtles" animated series (No. 10). Three more entries in the top 10 can't be officially classified as children's tapes but in many cases were probably purchased with young viewers in mind: "New Kids on the Block: Hangin' Tough" (No. 2), "Batman" (No. 6) and "Who Framed Roger Rabbit" (No. 9). Only the fourth-place (and R-rated) "Lethal Weapon 2" made the list solely on adult sales.

The sales recap also points to the overwhelming success of two likely if unfortunate candidates for the 1990 time capsule: New Kids on the Block and Teenage Mutant Ninja Turtles, each showing up three times in the list of the top 20 sellers. Because the rankings reflect sales from last January, tapes released early in the year -- or late in 1989 -- naturally outranked those heavily promoted low-priced tapes that reached the market in the last few months, the highest ranked of which was "All Dogs Go to Heaven" (No. 21). "Pretty Woman," the current top seller (and 1990's No. 2 box office hit), reached only the 70th spot.

The big-screen success of "Ghost," "Pretty Woman" and "Home Alone," the year's top three box office successes, came as a surprise to many Hollywood types who had banked on bigger numbers from the special-effects fests that dominated movie marquees this summer. Perhaps they should have kept a closer eye on the video rental charts, where comedy was clearly king -- claiming six of the top 10 rental slots for the year. And there were more surprises: While the No. 1 rental title, "Look Who's Talking," was a big-screen blockbuster by any standards, the same can't be said for No. 2 "When Harry Met Sally ...," No. 3 "Parenthood," No. 4 "K-9," No. 6 "Steel Magnolias" and No. 8 "Turner & Hooch," all of which outperformed movies that had higher grosses in the theaters. "Dead Poets Society," "Sea of Love," "Black Rain" and "Internal Affairs" rounded out the top 10 rental list.

Choice Ladies

When MGM/UA Home Video was folded into Warner Home Video, many fans of old movies had cause to worry that MGM's steady stream of film classics on tape might be halted; Warner has traditionally focused its energies almost exclusively on more current fare. It's too early to see what Warner will do with the treasure trove of film history it has inherited, but in the meanwhile it looks as if Turner Home Entertainment will be more than happy to fill the gap with its own offerings from the RKO Pictures library, which it controls. This month Turner will offer RKO Classic Ladies, featuring star turns by stellar actresses, including these films new to video: Maureen O'Hara in "At Swords Point" (1952), Irene Dunne in "Bachelor Apartment" (1931), Lucille Ball in "Beauty for the Asking" (1939), Merle Oberon in "Berlin Express" (1948), Joan Fontaine in "Born to be Bad" (1950), Rosalind Russell in "Sister Kenny" (1946), Ginger Rogers in "Tom, Dick and Harry" (1941), Bette Davis in "Way Back Home" (1932), Constance Bennett in "What Price Hollywood?" (1932), Claudette Colbert in "Without Reservations" (1946) and Maureen O'Hara and Gloria Grahame in "A Woman's Secret" (1949). The films are due in stores next week, priced at $19.98.

Take Five

New Year's resolutionaries who are already having trouble finding time for all that exercising they promised they would do no longer have an excuse. Wood Knapp Video has come up with the "The Five Minute Workout," which promises to relieve stress, muscle strain and general torpor in just five minutes a day; the $19.95 tape, on the other hand, takes an hour to watch. Consumers can also get a $3 rebate that will help them live up to their resolve to eat more of tape hostess Sandy Duncan's favorite crackers, Wheat Thins.