Yang Cheng Lake is a famous lake of Kunshan that most people visit (either to take a walk or buy some fresh crab) when the come. It's a huge lake that flows through many cities so there are different parts that vary from area to area.
Probably the only place in Kunshan for sightseeing. You have to pay to get in if you aren't Chinese and I think its about 40 RMB for adults, 20 RMB for children. You must hike to the top of the mountain because you can see all of Kunshan from there. Its also a very nice hike that takes about 15 minutes. Children can easily make the hike with you. I recommend walking up the old stone steps then descending by the windy walking path. This will take you all the way around the mountain and its quite peaceful. There are birds everywhere. Wander around the park and have tea in a pagoda. Take the kids to the small amusement park with rides for 2 or 3 RMB. There is a playhouse that is great for the winter thats 20RMB for basically as long as the kdis want to stay. There is a small zoo, an even smaller aquarium that runs through the inside of the mountain and comes out on the other side that has a little sea lion show every few hours. There is even this silly dinosaur cave walk that is a little scary for younger children but fun for older ones. Its only a few RMB. You can take a paddle boat around the pond and play on the beach. There are some bumper boats too but I haven't tried those yet. Looks like fun. Plenty of romantic spots and picnic spots as well as snack shops all along the way. You can easily spend 4 hours there and have a nice day. If you still have energy Ting Ling Road has great shopping and lots of cafes and restaurants. Have fun in Kunshan!
Bowling - the locals here takes it very seriously. They would eat a small snack right before and then eat a late dinner afterwards.
Very relaxing park at the north of the city. Interesting children's activities and a great view of Kunshan City.