Some children don't know how so need a gripping mechanism to teach them how. Also, some kids chew on pencils and perhaps do other weird things. How about you as a child?
I remember a female classmate in the first grade who was always chewing on the pencil. It's a good thing that I did not imitate her because she was harshly reprimanded when our teacher saw her. Germs, bacteria, the usual litany of adults on erring children regarding hygiene and sanitation. The best lesson for children in grade school is to teach them the purpose of the pencil and let them know that the graphite can be poisonous.
I didn't know about the graphite thing. Maybe that's what's wrong with me now, har har. Anyway, I always knew about lead being poisonous, but the term lead pencil is misleading.
Actually most us of thought that pencils had lead but the fact that graphite replaced lead as far back as 1550 or little later and graphite used in pencils is not as dangerous or toxic us most of us would believe. However, any foreign particle (including thumb) in mouth is not good as a habit or manners. So it's better if children learn to avoid it right from the beginning.
I still chew on my pens but I cannot imagine chewing on a pencil, but I suppose kids will put anything in their mouths. I do remember kids eating and chewing on erasers, so maybe that is more of the danger, but either way it is something that might need a little guidance.
I know some adults who still suck their thumbs. Anyway, that would be a good title for another post. Why do you think they do - or should we make another thread?
I can't recall any bad habits about pencils when I was a child. I used a large pencil in kindergarten which was quite easier to control. I wasn't the type who would put pencil or eraser on my mouth. I didn't know other people have issues about holding pencils until I had my son who happens to be a lefty. It was a struggle to teach him how to write properly using the standard writing strokes. I can't even see how he was doing it but as long as he produced the letters and numbers, I've decided to let him have his way. His penmanship is actually better than other kids' handwriting. It didn't help that his school wasn't ready for left-handed people like him and all desks are of the standard type.
In my case I don't remember that I had difficulties in holding my pencil, although I ended up being left-handed than the more common right-handed.