now, now

1 The words Now, now... are commonly used to call people to order when it sounds like things are getting out of hand. It has a special intonation in this usage — a singsong quality whereby the first now has a slightly rising intonation and the second one is short, hanging and somewhat stern. 

In this snippet, Nicky can tell that if he doesn't take charge of the situation, things are going to get ugly, so he uses now, now to mean «calm down — let's not get excited».

Nicky walks into his sons' room to find them fighting over something.

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Danny: How many times do I have to tell you... I don't have your ball!

Billy: Because you hid it somewhere! Give it to me or I'm going to put bleach in your fish tank!

Nicky:  Now, now, boys. There's no need for threats. If Danny says he doesn't have your ball, he doesn't have it. Didn't you have it in the car this morning? Go look in the car. I bet it's there. 

2 When spoken with a soothing tone of voice, now, now is used to console someone who’s crying. Here, the first now is steady and the second one has a slow, sympathetic, falling intonation.

Ben gets a call from his daughter, who’s at the animal hospital because her dog got hit by a car. He finds her in the waiting room, and when she sees him, she starts crying.

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Angie: Oh, daddy…

Ben: Now, now, honey. The vet just told me it’s just a fractured leg. He’ll be in a cast for a while, but he’ll be fine. You’ll see.