This article clearly explains how Archimedes calculated Pi – the constant ratio of a circle's circumference to its diameter – over two thousand years ago. Read this article and then explain it to your kids. They will be fascinated.
From the LA Times: "Backed by $20 million in venture capital funding and building off recent advances in robotics and precision manufacturing, the Culver City company [Bionaut Labs] is developing a device the size of a breadcrumb that doctors can insert into the spine or skull and magnetically steer to a target to deliver a precise dose of drugs. The plan is to move to clinical trials by 2023."