It can be hard to sit still, and many kinesthetic learners will tell you it helps them concentrate to have some kind of movement to do. Some scribble during lectures, some do fancy pen twirling, and more and more folks knit.
There are many educational methods that teach children some kind of handwork: Charlotte Mason, Waldorf, Montessori, and others. Doing something with your hands was something I was taught as well, along with an attitude of "never sit idle" that encourages me to sew or knit or embroider while I watch TV or sit and listen to our read alouds at night.
For little kids, having something to do with their hands has many benefits. They are learning coordination, concentration, and focus. It can also help little squirmers sit still and listen while you read to them. Carbon's current handwork is the knitting mushroom, and he did enough with some of my old yarn that he got to go to the yarn store and pick out his own ball of yarn - he selected a lovely bright red wool.