Is this a first come, first serve park for parties or can reservations be made?

Yes, it is 1st come 1st serve, however you can do what we did 4 our granddaughter's birthday a couple weeks ago. We brought a couple tables of our own...

I am pretty certain it is first come first serve. Weekends are busy so may be difficult to get tables. If possible I would plan for a weekday. Most people there are very friendly and would likely let you have a table they are using if you ask.