If there is a place that I like to go for a good weekend, it's Amphawa. Amphawa is a floating market, but a genuine one that's mostly used by Thai people. What I love is that even though there are a lot of people, the atmosphere is really Thai, lots of street food, people singing karaoke here and there, restaurants and cafes in old wooden houses along the sides of the canal...
If you are traveling with your family, a trip up the canal crossing the town will please everyone, especially in the evening when you can see all the fireflies hanging in the trees like so many Christmas decorations.
For the day time there are, (as always in Thailand), several temples. If you only want to visit one, then make it Wat Bang Rung, a small, ancient temple covered by a tree. I saw lots of Thais going there to show their respect to Buddha.