I came across this project a while back, but I've been saving it for when it made more sense to be celebrating spring. Rubber bands make a great power source for lots of homemade toys, and this riff on the ornithopter will bring a regular greeting card to life in an unexpected way.
Youtuber Natalia's Toolbox starts with a template for wires and paper cutouts, and gathers a few other tools. Arguably the toughest part of the project is cutting and twisting the wire to fit blueprints. There are a few fine bends that might be difficult for a younger person to do without some help. One cylindrical section will make up the body and engine, with the other "flapping" the wings. The wire assembly comes together with a regular rubber band, and then the various wing segments are glued on. Natalia goes above and beyond in decoration by also drawing in wing markings once the butterfly is constructed, but I think the actual wing action might be impressive enough, personally.