The Liberal premier was on the road in the Windsor area and Cambridge, and was to visit Thornhill later in the evening as she attempts to win the June 12 provincial election.
After a stop a Toyota plant in Cambridge, Wynne got on the media bus with reporters following her campaign with a box of cupcakes in hand.
She says it's an old Dutch tradition that on your birthday you take a treat to work.
Staffers sang the premier "Happy Birthday," but when they got to the line "happy birthday dear premier," she exclaimed "Kathleen!"
Wynne's partner Jane Rounthwaite then boarded the bus with a gluten-free red velvet cupcake for the premier, who before blowing out the candle said, "OK, I get one wish, right? Guess what it's going to be."