Buddy used to do the same thing with my boys. Now, Buddy has to have a toy in his mouth before he can chase the boys around the yard. This keeps him from nipping and jumping at them. The boys know not to run until they plop a toy in his mouth, and the funny thing is is that Buddy now knows he has to go grab a toy before chasing them. It's pretty funny. These dogs are almost too smart.
I had mentioned this issue to our trainer and she suggested having the kids run with one of the dog's toys and throw it when the dog starts to get close. That works, too.
Another thing I do is teach "off" (meaning all four paws on the ground) and the second I see Buddy look at one of the boys like they're a long lost littermate, I will say, calmly, "Buddy, off!" And that breaks his concentration of them.
You do definitely have to be out there supervising when the dog and the kids are together, at least at first. What is so surprising to me is that Buddy is now absolutely perfect with my youngest, who is 5. I'm trying to figure out if my youngest has a different energy than my 10 year old, who Buddy likes to play with very roughly. My ten year old is more energetic and loud. Crazy loud.
So I have to be there when he and Buddy are out together always (for now.) I am constantly reminding my boys to stay calm, and that will keep the dog calm.
Our latest problem is the swings. Buddy put holes in two of my boys' shirts yesterday trying to "catch" them as they were swinging.
So today I'm going to go out and put him in a sit/stay while they are swinging and continue to do that until he learns to leave them alone and stay away while they are swinging.
Good luck!! I know it can be frustrating.