Finely chop milk and semisweet chocolates and place in a microwavable bowl with cream. Microwave for 2 1/2 minutes at medium (50 percent) power. Stir until smooth. If chocolate still hasn't melted, continue to cook it at 30-second intervals, stirring in between.
Place berries, pretzels and marshmallows in bowls or on a serving plate. Reheat chocolate mixture, if necessary, for about 30 seconds on medium. Remove, and serve with the accompaniments.