Recommended length of stay: 1 day.
Things to do:
River/canal boat tour. There are 2 to 4 hour options, but 2 hours is more than enough, if you are not willing to visit every temple and feed the fish for half an hour.
Khaosan Road (backpackers street) good thai food, cheap massage, lots of people. Cheap hotels around 30usd.
Lebua hotel – is famous for its restaurants. (be careful many of them do not allow with children until 14years old) Dinner cost ±100 usd per person. If you are on a budget – i recommend you visiting a sky-bar and have a drink (15usd) then go eat somewhere else. Great breakfast. (there are only 2 places that i remember about breakfast: Lebua and Rye Juan Carlos in Barcelona)
Baiyoke hotel – do not recommend. Tallest building in Thailand, but the hotel is less than average 3*
Aetas Lumpini – 5 star hotel for a 3 star hotel price. Stayed few times there.
Conrad Hotel – one of very few hotels in central Bangkok with a tennis court. Has good restaurants and breakfast.
do not ride TukTuk, unless for an attraction, because they are rather expensive at the end..
taxi is cheap in Bangkok and you should always pay what is written on the meter. Never negotiate with taxi driver (only tourists negotiate) just sit in and drive, at the end you pay what the meter says.