Thumb sucking:
http://uwphysicians.org/hbeat/hb990831.html

Children - pacifiers, thumbsucking http://www.saveyoursmile.com/parents/dpacifier.html

Thumb sucking help books:
http://opport.unety.net/thumbco/thumbs_up.htm
http://www.amazon.com/exec/obidos/ts/book-reviews/0961478020/top100/102-8259226-9002420