In addition to creating a SignUp of shifts to work and items to bring, you can also track the total number of people who plan to attend your event.
Setup a Spot to capture RSVPs.
You can limit the number of people who can RSVP or leave it at "any number of". The spot will be to "do or attend". You can also add Extra Details to direct participants:
Note: You can force the RSVP spots to display at the top of your SignUp by either setting it's start time earlier than other spot's start times, or leaving the time setting to "at anytime".
Last, you can also separate Adult and Child RSVPs, as shown in this particpiant-view: