Cut them out of 11x17 white paper, folded in sixths. I would buy a heavier weight of paper than copy paper and it is rated in pounds.
I would then use sewing thread and a needle and piece one end of the snowflake, knot that end and then cut the thread to length.
I would use heavy gauge sewing pins, or push pins on the ceiling, to hang the thread.
Ensure your pins are solidly fastened into the ceiling. I would ensure they are high enough to keep kids from jumping up and hitting them.
You can use fishing line in each snowflake and attach to the ceiling with push pins even heavy duty straight pins will work.
Valerie...You can use clear beads and pipe cleaners.