My children are familiar with the number Pi because we read these great books that introduce math in a fun and informative way! The books are part of the Sir Cumference and Knights of the Round Table series.
I casually mentioned to Sean that it was Pi day and I was going to make an apple pie for dessert (I had an apple pie in the freezer). He said that he really wanted Key Lime Pie. I have never made Key Lime Pie before and did not even know he liked it, so after an Internet search I found a recipe that I only had to go buy 4 ingredients and proceeded to make a delicious Key Lime Pie.
After desert was over, Sean said that is not what he remembered Key Lime Pie to look like. I discovered later that what he really wanted was Pistachio Pie (which is made with jello pudding and dream whip ~super easy!). O Well, It was delicious and satisfied my husband that I was willing to make a special pie for him.
Sean did a mini lesson showing the children how to measure pie and then challenged them that if they told him the diameter of something he could tell them the circumference without using a calculator or paper.
He had them measuring like crazy and figuring out if he was right and the children were thrilled when he missed a number by something crazy like 1/2 cm. He was pretty impressive.