Cut cake horizontally into four equal layers. Place bottom layer on a serving plate; spread with half of the strawberry ice cream. Immediately place in freezer. Spread second cake layer with vanilla ice cream; place over strawberry layer in freezer. Spread third cake layer with remaining strawberry ice cream; place over vanilla layer in freezer. Top with remaining cake layer. In a bowl, beat cream until soft peaks form. Add sugar; beat until stiff peaks form. Frost top and sides of cake. Freeze until serving. Decorate with mini flags if desired.