In kindergarten you can grow a bunch of interlocked small crystals. It's difficult to make a nice big one, as a sibling comment complains.

(We made a big one in high school, but it was AlK(SO4)2 instead of NaCl. They have a different shape. I'm not sure if they have other properties that make it easier. Kids may drink or eat it, I'm not sure if AlK(SO4)2 is safe enough for kindergarten. It was a side project that took a few month.)

The article here is the "advanced" version that is necesary to make big crystals. These kind of stuff usualy get traction here since forever, so it's not surprising that it got to the front page (multiple times). (Bonus points for nice photos.)