I'm familiar with elephant parks in Northern Thailand, near Chiang Mai. Are there any good elephant parks (preferably with humane treatment) within a day trip's distance from Bangkok?
I stayed in Hua Hin about 2 years ago, and went on a trip to see elephants right outside of town. I believe the park at this link is the correct one: http://www.thailand-huahin.com/huahin-elephants.htm
Hua Hin is approximately 200km south of Bangkok. I cannot attest to the treatment of the elephants, but everything appeared on the up and up when I was there. I remember this park as being family friendly and enjoyable.
I hope this helps. If you need any further information, just ask!