If you have never been to Thailand and you only have 2 weeks, you need to do some careful planning to get as much out of your trip as possible. If you have children need to plan activities around them.
Besides Bangkok, there is a host of islands in the south and mountain areas in the north.
You really need to plan what you want to see.
Islands give yourself 4 days to do the Island Hopping tours and see Maya Bay and all the other beautiful islands. Ao Nang is a good base for that.
Bangkok 3 days, including an evening visit to the famous Chinatown and Khao San Road.
Kanchanaburi is an awesome location for Erawan Waterfall, the Death Railway and the Bridge over the River Kwai. 2 days.
Head north to Chiang Mai, Chiang Rai, Phu Chi Fa (A must see) (1 day travel and 3 days stay = 4 days total).
Back to Bangkok, spending some time in Ayuttaya and Bangkok Shopping!
If you work out the travel, or air travel from the islands (Phuket) to Chiang Mai, you might have even more time!
You can plan this trip yourself, do your own research so you are not disappointed by others advice!