At my son's school the birthday child got a special crown to wear all day... the children all sat in a circle and the song "The Earth goes around the sun, the sun, the Earth goes around the sun... 1 year... 52 weeks... 365 days." while the teacher stood in the center with a candle and the birthday child took a globe and walked around the room inside the circle. Every time they came round full circle the kids would shout the right number "year" (1,2,3,4,5,6). Then when it was the "right" number the child would stop... everyone would yell "Happy Birthday!"... and the bday child would get to make a wish and blow out the "sun". Then cupcakes were handed out as they went out to recess. The parent would stay until the end of recess / all the cupcakes were eaten... and the kids would go inside for lunch.
The preschool teacher found it "best" to have an extra recess before lunch to run off the cupcake sugar and then fill up on real food.
It was a really touching and cute ceremony. Children who had their birthdays over breaks either celebrated their 1/2 birthdays... or on a day toward the beginning of the break.