According to a new book titled "NurtureShock:  New Thinking About Children" 
there are two sentences parents should use if they wish to get the truth from their kids.

Lets face it, we have all lied to our parents once or twice when they asked us about something. Now, this book title "NutureShock" suggests that if parents use two sentences when trying to get something from their kids, the parents will most likely get the honest truth.

The two sentences the book recommends parents use are: "I won't be upset with you if you did it.  And if you tell the truth, I'll be really happy."

Erick Barker, the author of the book, says those sentences significantly cut down on lying because, quote, "Young kids are lying to make you happy, to try to please you." He also suggests that parents tell their kids, "I'm about to ask you a question.  But before I do that, will you promise to tell the truth?" prior to questioning them about something.

I totally get it. I think if parents are straight forward with their kids prior to interrogating them, we as parents are more likely to get the honest truth from our kids. Instilling fear in kids does not guarantee we will get the truth from them, but reassuring them betters the chance. Maybe this is something we should all consider next time we approach our kids.

Source: Lifehacker