Wildflower seeds! Bonus if they’re native to the state/area. Packets cost a couple bucks. Add a small terra cotta pot for another couple bucks, or DIY some seed bombs and wrap them in a piece of fabric cut from a shirt/sheet/whatever you are considering discarding anyway, tying with a contrasting color of thin fabric.

For the kid in your family, I would suggest researching the wildflowers native to their area, and writing out or printing directions for them to make the seed bombs themselves. Maybe giving parents of said kid $10 to purchase soil for the project.