We’ve been making slime at Gravenstein (where I’m known as Mr. M), and students are bringing a bag of slime home. We are just using washable school glue and cornstarch, sometimes with shaving cream and food dye added in. The recipe below includes Borax, which we aren’t using since it can be a skin irritant. If you want to make your slime thicker at home, you can try adding warm water, baking soda dissolved in warm water, or contact solution.
https://www.pbs.org/parents/crafts-and-experiments/homemade-gak