I don't always have a theme but if I do, it is a monthly theme. So for example January I will work on Snowmen, February Valentine's Day, March St Patrick's Day, April Spring, May etc ...

I agree with Playfelt in having repetition and adding to a theme each year. I only have 9 themes per year because I don't do any programming in July and August.

I have a purchased toddler theme from http://adaycare.com/ and I find I still resort back to my own materials and planning because even with a purchased theme I still made adaptations and still had prep work.