It would be a fun project for kids (with adult supervision of course.) Cutting out part of the top of the plastic bottle for planting ends up leaving a raw edge but I'm thinking something could be figured out to cover the edge so it wouldn't be so sharp. I'm not very creative and I thought about just using a thick bead of hot glue all along the edge but got lazy and ended up leaving it ragged.. I did wear gloves when planting though because I'm the worlds worse klutz and would have cut my hand on that jagged plastic for sure.
I looked around for something to plant in the top ... don't have any cactus but found a pot of Haworthia on a plant stand so I took some of them to plant in the top. I prefer the look with the cactus as Woodspirit showed in her photo ... a much more spiky hedgehog look so I might change the plants out if I ever get a chance to go shopping for some spiky cacti.
Here's a couple of views of the finished product; "Mrs. Hedgehog":
