The child has told us what happened. (But it took a while.)
The child hasn't told us what happened. (We're still waiting.)
The child has told us his account of what happened.
The child is telling us some of what happened. (We're listening for the rest).
"a story" – an expression meaning an untrue account (description), inaccurate, an explanation substituted for the truth.
"we're not buying it" – an expression meaning someone doesn't believe what is being said.
"Oh, Really." By David Kessler. Flickr, 6 Apr. 2005. flickr.com/photos/plasticrevolver/46453652. Licensed by CC BY-SA 2.0. Accessed 21 Nov. 2019.