depend on the age group, your son seems pretty young yet, are the rest of the kids about that age or little older?
i have done preschool for years and have found circle time really motivates for the rest of the days activities, just depends on the age group though, if you try too much too early, they just dont care. If they are younger, I would just stick with a simple game or funny rhymes. but if they are 3's or near and up, you can start daily "routine" things that really pay off really fast. I always do the days of the week song ,and the months of the year, and even with young ones you can do quick flash cards of the alphabet and numbers colors too. your sons age can do alpha, number, and color memory and circle time is a good time to do it. every day....he will know alot in no time at all!!!! kids are SOOOOO smart and pick up quick.
NOTE: for circle time rugs I go to the carpet store and ask for the sample pile, my local carpet store sells me the small samples(about 18x24inches) for 1$ a piece and they make kick butt circle time rugs, and I choose them in all dif colors, being samples there is an endless array of colors to choose from. that way each child gets their own rug and YOU can place it where you need to and explain they do not leave their rug, to the ones who like to move or bug others. good luck