[tenderfoot]

It is your job as the leader to create harmony in the pack. So you must teach this pup that you will not tolerate any form of attacking the other 'pups'. Right now the puppy doesn't respect your word, because she knows you have no power - she can out run you and is faster than you. The leash gives you the last word.
Put the puppy on a long leash and get the kids to start playing at a low level of energy. The second the puppy thinks about leaping for an ankle or pant leg, give a slight correction on the leash and say "leave it" or "quit" in a very firm tone - you can even rush at the puppy with energy and back her away from the kids. Allow this to happen a few times - until you can say the command and not use the leash. Now the puppy is repecting you and choosing better behavior.
However if you are doing this a dozen times and the puppy is not stopping then you need to increase your intensity (not loudness). You need to impress the puppy with your word and energy - otherwise it is a game to her.