Talking to them won't help. They will only leave the playground when you repair the school bell and ring it. Then you can dig where they are standing.
(see the related questions)
On Big Nate island the three girls stand on the playground to the right of the school .
its where the talking girls are standing
near the playground
Under the playground
where the chatty girls are.
The Treasure is on the ground where the girls that are ignoring you are
at the playground
its where the girls were "yakking"
in the middle of the girls on the playground!
under the girls at the playground.
Somewhere on playground
The capsule is beneath the school girls on Big Nate Island Poptropica.