there's a good boy, girl, dog, etc.

there's a good boy/girl

1. Used to encourage or give praise to a child or animal, especially a pet. Go help your mother clean the dishes; there's a good boy. There's a good girl! Now, stay.
2. Used to give condescending, patronizing, or belittling praise to someone. Now, go tell your boss that I need his signature on this docket; there's a good girl. Fetch me a cup of coffee, will you? There's a good boy.
See also: boy, girl, good
Farlex Dictionary of Idioms.

ˈthere’s a good boy, girl, dog, etc.

(informal) used to praise or encourage small children or animals: Finish your dinner, there’s a good lad. Sit! There’s a good dog.
See also: good
Farlex Partner Idioms Dictionary
See also:
  • do no good
  • for good measure
  • be as good as new
  • do (one) a/the world of good
  • as good as it gets
  • (one) (has) never had it so good
  • be in good condition
  • (as) good as new
  • as good as new
  • come up to expectations