This is actually an activity we did a few months ago and I never got around to posting. I thought it went great with the letter B theme we've got going on though, so I went ahead and included it, despite the crappy quality of the cell phone pictures. I found this fun idea here. It does take some prep work, but there's no reason why your little one can't be involved in that aspect of the fun too.
Erik loves helping out in the kitchen, so getting to help make the goo to roll the cotton balls in was a big hit. He does have a thing against getting his fingers messy though (unless we're painting, go figure...) so he was not interested in actually rolling the cotton balls in the goo.
Once the balls were done cooking, they did have some sharp edges. I took some scissors and clipped those off as best I could and we just went for it.