My three year old really got into this activity. First he sorted by object, putting all the jelly beans in one container, all the buttons in one, and so on. Then, because he was really into the jelly beans, he decided to sort the jelly beans by color. He did find the tweezing difficult, and ended up using his fingers for most of the activity, but still gave the tweezers a go for a little while. When he was ready to put everything away, I had him experiment with which objects were easier to tweeze and which were more difficult. We discovered that the rough objects (like the cloth buttons and the Cherrios) were easy to pick up and the smooth objects like the beans were more difficult. This led into a discussion on texture.
My two year old really couldn't do the tweezers, though I did encourage her to try. However, she absolutely loved sorting! She sorted all her objects three times before getting bored! I noticed as well that she put the jelly beans and kidney beans in the same compartment, meaning she was sorting them in the general category of "beans", while my 3 year old was able to distinguish two more specific categories of "jelly beans" and "kidney beans".
This activity is so great for so many reasons. Not only is it fun for your kids, but it provides some wonderful opportunities to fine tune their pre-math skills. Spend time talking and experimenting with different ways to sort the objects and take the opportunity to talk about texture and shape, letting the children explore the different objects with the fingers. The tweezing aspect gives them a chance to work on those fine motor skills which will be so helpful once they start writing and drawing.