I’ve frequently had cause to try and meet people in the Blue Mountains in a kid-friendly place, and I’ve found it surprisingly hard to do so. There’s teeny playgrounds of various types. There’s all the big tourist attractions which might work for older kids but about which mine couldn’t give a damn.
After poking at a map for a while, I discovered Wentworth Falls Lake, which seems to hit a decent amount of criteria for people with little kids. There’s two small but not uninteresting playgrounds, a number of fairly level and even paths, picnic tables scattered about, electric barbecues and a sheltered eating area, general space, and a decent-sized (albeit unfenced) bit of water to please the eye:
I’ve apparently managed to catch the train past this about 50 times without realising that it was a place worth remembering.
Note: it’s in the town of Wentworth Falls, it’s not at the actual falls. It’s on the north of the highway, the falls are on the south.