Use of plastic bags is a major threat to the eco system - Would you like to dress her up in a Bag shaped Dress where you can talk about using eco friendly bags that can be reused, recycled and are bio degradable. Also You may dress her up like a PAPER BIN - Where you are sending a message to collect all the small and big sized paper in the form of Receipts, tag, Paper bags, Bus tickets and then can be recycled.
Its a fashion show, whether its for elders or kids a fashion show is a fashion show and don't make it into a fancy dress contest, both are different, so concentrate over the kids costume which fulfill the eco friendly norms for kids.... Eco friendly costumes may be designed with two functional things...... The first one is think about the costumes functional properties towards external factors like light radiation, air permeability, water permeability, dirt proof etc.... 2. the impact of the costume towards nature, that is the method of disposal, properties of dyes and other chemical agents emitted from the costume towards the nature.. So if you want your kid to win think something different not as usual from others do make..... I have a nice idea for ur kid... design a rain coat for ur kid in jute... Jute being eco friendly in nature, first bleach jute once or twice using a home bleaching powder, allow to dry, then add colour using normal acrylic colour in water, then dry well and stich the rain coat, finally apply wax coat by melting wax and dipping the rain coat over it, after drying crush the material well and there it is a wonderful waterproof rain coat for ur kid in eco friendly jute