Here are the correct placements for the phrases:
A child on a swing. a. is a translation
A child going down a slide. a. is a translation
An apple falling from a tree. b. is not a translation
A baseball bat being swung. b. is not a translation
A child doing a cartwheel. a. is a translation
This categorization is based on whether the actions imply a physical motion or change of position (translation) or if they do not.