New Zealand's oldest botanic garden
This is such an expanse of places to play and explore, you will need some time. I would say, come back on several occasions and enjoy all seasons this place has to offer. A great kids playground, train rides for kids (on Sundays), a massive glasshouse with tropical plants, a cafe, about 28 hectares of garden, trails, an aviary, the list goes on and on.
Directions
The gardens are huge, with multiple parking lots. There is also heaps of street parking right around them. I would recommend to make it easy, park in the lower parking lot that comes off of Cumberland St. Or at the parking lot of of Lovelock Ave in the upper gardens.