Seems like normally puppy behavior to me, too.
1. Having the puppy on a leash will allow you to put an end to that quickly.
2. Teach the puppy to redirect to a toy and not kid's ankles... as soon as you see the puppy LOOK at the kids and start to bunch into a chase... yell "BALL" (or rope, or any other toy name) and then YOU run after the ball, and get the puppy to chase YOU... and then grab the ball for a game of fetch with the ball. Once the puppy is focused on the ball, you can have the kids join you with teaching the puppy 'fetch', 'release' (or 'drop') or any other game commands you want to teach her.
3. Teach the kids that if the puppy comes after them, to herd them or nip at their ankles, that they need to STOP and NOT MOVE... moving is excitement. To stop the puppy's excitement, the kids must be BORING. They should just stand still with their arms crossed, not even looking at the puppy. This is teaching the puppy that inappropriate play = game is OVER. You'll need to be there to redirect the puppy again, as needed, too.
Aren't Puppies FUN!!?!!
The work you put in now will really pay off later, though. Be calm, consistent and generous. Catch your puppy doing good things with LOTS of random rewards (treats, praise, love, etc.), and they will do more of what you like. "Yelp" (or "ouch!") and redirect away from unwanted behavior to teach your puppy what not to do in a reaffirming manner. This is a baby, don't forget, still testing and learning about the world around her. Help her explore with confidence and love - and it will come back to you in multiples!