Customize horse blanket
If they all have horses, then they have horse blankets (in Michigan were it gets cold), each kid could customize their horse blanket with the horses name (maybe add a stock 4H logo with the name).
One simple way to do this, is by making a reverse vinyl stencil and using regular Krylon black spray paint (or white on dark blanket).
You let each kid typeset the name of their horse on the computer, letting them select the font they like.
Then you let them watch the plotter make the stencil cutting out the names (you can gang them to cut several at once), using some cheap vinyl.
Now comes the fun part, you cut the different templates apart and let each kid weed there own template and apply the app tape.
Then each kido, will position the reverse stencil mask onto the horse blanket, then using the black Krylon spray paint, they spray paint the name/logo onto the horse blanket, best to use several light coats.
The Krylon spay paint dries very fast, remove the stencil and presto, your kido has a customized horse blanket with the horses name and 4H logo or the owners name etc. And they learn about the different steps in making signs.
I know it's not like the high $ embroidered horse blanks, but this is a good project for them to learn
I have use this process on many outdoor fabric type projects myself, and the finished product is flexible, doesn't peel off and last a long time.