Melt butter in a saucepan over low heat. Add marshmallows and vanilla extract. Stir in food coloring. Add rice cereal, 1 cup at a time, stirring after each addition, until blended. Scoop out mixture and shape into small pumpkins using buttered hands.

Cut string candy into stems and cut fruit roll-up into leaves. Decorate pumpkins while still soft. Let cool completely, at least 20 minutes. Draw faces onto pumpkins using decorating gel.