Line 3 large baking sheets with wax paper. Pour cereals into a colander; sift out small pieces.
In a large bowl, combine cereals, marshmallows and raisins.
Heat a medium saucepan of water to simmering. Place white chocolate morsels in a glass or metal bowl and place over simmering water. Heat, stirring, until melted, about 3 minutes. Cool slightly.
Pour white chocolate over mixture in bowl; stir until all dry pieces are coated. Working quickly, drop by heaping spoonfuls onto prepared sheets. Let stand at room temperature until dry to the touch, about 25 minutes.