She's just a puppy, it's very hard for her to focus. Plus, she's a Boston and Bostons love people. Hearing these kids play and not be able to go see them must be torture for her.

In general, dogs are better at doing their business in quiet environments, let alone a puppy.

This is totally expected behavior. You'll just have to find somewhere else to go. Don't forget you don't want her to get used to doing her business in just one place, because then you'll have a big problem on your hands !