So, my daughter wanted to be a Lake Monster. We dig into the stash, find the ugliest green fabric we can, and threw together this costume. We also used aquarium plastic plants and various rubber bugs and critters. I loved when we were digging through some old boxes in the barn and came upon the box of aquarium plants, she looked up at me and I could see the wheels turning! I may have a crafter kid yet! She did win her grade's costume contest.
My son was a train engineer, which was super simple. I only had to make him a hat and find some overalls!