Parents MAY HAVE difficulty stomaching the clearly commercial nature of Expert Software’ s McDonaldLand CD-ROMs ($14.99; 800-759-2562), but children will eat them up. With names like Silly Games, Jump ’n’ Slide and T-Shirt Fun, it should be obvious that none of the discs in this six-title series is designed to be educational. They are meant to be fun, and they are. And when your children are done playing with Ronald, Grimace and the Hamburglar, there’s a coupon for a free Happy Meal with each disc.