is it possible to get all the list of folders that a particular group has access from child level?

 yes it is possible to fetch a Group's collaborations: https://box.dev/en/reference/get-groups-id-collaborations/

 the API returns only parent folders, I am looking for something which can give me list of all folders and subfolders as well. 

Any kind of help is highly appreciated. 

  ah, ok. That is currently not possible with our API. You would have to traverse each folder to get the full folder tree under that folder.