I am currently reading Sharifa Oppenheimer's book, Heaven on Earth: A Handbook for Parents of Young Children. In it she talks about outside activities. (The book, by the way, is great for anyone interested in Waldorf education in the home). She writes: "Swinging and rocking motion both gentle and vigorous, stimulates proper brain growth and "wires" the different areas of the brain together." After reading this statement, I recalled the time during my Montessori internship when I was told about the positive effects that rocking chairs can have on children. We had a rocking chair in the room that was frequently used. Children sat in it at anytime during the day when they wanted to and it was enjoyed by everyone. My professor always said it slowed the heart rate and released endorphins which elevate the child's mood. Rocking chairs also have been shown to provide a calming effect and relieve pain. In Sharifa's book, she suggests having a swing, hammock or seesaw outside and a rocking chair inside.
Here are two examples of activities we have available in our home which involve rocking. This first is a balance board. Balance boards come in different styles and some are easier than others. This one is great for my "nearly" two year old. It is too easy for her older sister so eventually I would like to get a more advanced one when this one is outgrown.
We also have a fantastic rocking moose that gets used almost daily by both children. They do some vigorous rocking on it and it nice to have on those days when we are stuck inside due to the weather.
...And of course, there is always holding them and rocking. They never seem to tire of that =)