Colonial Drive, Franklin NJ. Look for Mettlers Road, and the Somerset County Parks Website for directions and all the amenities this Somerset County park has to offer! Thanks Anthony B. for the recommendation! Nice quiet park, very nice grounds, and I’m sure locals can get you more details we were just passing by so didn’t get a chance to fully explore. There is also a touch and smell garden, can’t wait to revisit! And the paddleboats are something to look forward to this summer 
Please comment if you’ve been in this park. Attached are the pictures we were able to take.
Colonial park has a nice, shady playground with a fairly large sand box, walking distance to paddle boat rental and a minigolf course. There are ponds and walking paths, and several nice gardens (roses, scent, etc.) in another section of the park.
mini golf? I’m there!
We absolutely love Colonial Park, and are lucky enough to live really close by. In the summer, definitely check out the rose and sensory gardens, which have been closed since last summer for refurbishing. Also, there is an amazing perennial garden, in the same section of the park (across Metlars). My daughters and I try to visit the perennial garden several times a week during the spring and early summer to watch the amazing changes as the flowers bloom and grow.
Also, the walking path is a great way to get a post-picnic work out, as long as you don’t mind if your kids stop to “work out” at all the posts along the way.
We live about a mile from the park. The playground is great- there are climbers, slides and swings that are appropriate for both younger and older children. It can get fairly crowded in nice weather. Plenty of parking. Walking path is nice. Lots of open space to explore too (big open field is great for flying kites). Gardens are beautiful.
The D&R canal state park is adjacent to the west end of Colonial Park, and a footbridge has recently been installed so that you can cross from CP to the canal towpath- very nice!
Not a playground, but the D&R canal towpath (here off Colonial Park, and the other sections as well) is a great place to hike with kids. Flat, shady and always something interesting to see.
Today was our first time there, my daughter wouldnt let us leave the playground to explore the rest of the park. When I did convince her to leave (ice cream was included in the convincing) we were able to drive thru part of the park, it was lovely. A great place to take your children for a hour or a all day trip.