Good Morning Grams, to one Gr ma to another here I think a lot of kids put their fingers in their mouths. Remember biting fingernails ewwwwwwww or other not so wonderful things ;)
Our 2 oldest bite their nails, and I just remind them to take their fingers out of their mouths. Of course you can always get one of those microscopes at a Hobby store and put some dirt from under their nails on a slide and show them how nasty that can be. BROKE me from being a nail biter in HS!!
Our Mouths are full of germs any way so anything else in there just adds more stuff. I once saw a 24 y/o woman sucking her thumb, now that was g-r-o-s-s
Just keep reminding them Grams to take things out of their mouth. Wash hands frequently etc.
Good Luck, it could be worse, I heard worms are mighty tasty, and frogs are slimmy when ya kiss um too ;)
*laughing* at the memory
K. Happy Nana of 5