Position cakes on double-thick foil-wrapped boards. Pipe tip 8 bead bottom borders in buttercream. Tint 1 oz. portions of fondant pastel blue, green and violet. Separately roll out, along with reserved rose and yellow fondant, 1/16 in. thick using guide rings. Cut 1/4 in. wide strips for toy box trim; attach to box pieces with damp brush, cutting to fit as needed. Assemble box with royal icing; let dry.