The main thing is not to panic or scold them for it, or they'll want to do it even more 😅
Yes, this is a completely normal stage of development. Toddlers at this age explore everything through their mouth - it's not a deficiency or a disorder, it's just how they're built. Sand, fur, dirt - these are textures, tastes, sensations for them. Their immune system gets stronger, their brain develops. Of course, you need to keep an eye out and remove obvious dangers (sharp things, small objects, toxic stuff), but licking sand or eating a bit of dirt is totally harmless.
I knew a girl who at one year and nine months was literally eating handfuls of sand at the beach. Her parents were going crazy, calling the pediatrician every time 😂 The doctor calmly said it would pass on its own once the kid got bored with it. And sure enough - by age three it was gone. Now the girl is six, a completely normal person.
Here's what actually helps: offer safe alternatives (teething cubes, teething toys, crackers), watch them as much as you can on the playground, but don't stress too much. And wash their hands before meals - that's usually enough.