From the book How to Negotiate Like a Child [1]:

  once someone has offered something extra, it's hard to take that back.

Further:

  often when confronted by silence, the blabber will say something that
  she didn't plan on saying.

And further:

  if you observe children, as I did while researching this book, you'll
  notice that kids are content to sit with their friends and not say
  anything at all for periods of time that would drive an adult to
  reveal all manner of personal information.

[1] isbn:081447294X