Your Headmaster had me, when he was young and free
Years later, he had me a second time around
You can have just one, but numerous are we
If I am the wrong one, I can end up on the ground
If you ask me if I am small, my response would be "yup"
Be very wary, for I could make you puke
I am so tiny, many of me can fit in just one cup
If you want to find me, you can start at Honeydukes
What am I?