No, you can park on one of the side lots on the boulevard anytime. You'll also be able to walk the park whenever. They just have a gate closing the play area.

Unfortunately Trip Advisor does not permit attaching web site address. You can do quick Google search using Nomaheagan Park picnic reservations. You will see the ucnj site. They have the information you need as well as an online registration process. Also you can call the County Parks department at 908-527-4900 or 908-654-9805 Enjoy, and keep in mind I'm available as an extra guest :)

I believe its about 2.5 if you walk the whole thing, but there is also an additional park across the street if you want to add more miles, or if you want to make it shorter you can walk the inside paths near the water fountain only