From the event website:
"The event's collaborative, non-competitive atmosphere offers an alternate setting for students to explore the joys and power of mathematics with other kids and older mentors.
We provide the mathematics and mathematicians to work with the students on the activities. Please bring an adult to provide supervision of your children/students. Admission for kids is $10; supervising adults are free. If you can't afford the fee, there is a checkbox at the bottom of the form to waive it."
There are two sessions for kids in grades K-3 and two sessions for kids in grades 4-8. See the event page for more information and to sign up.