Using representational model, how do I get to the next level of the tree?

[dlmcshan]

I am trying to read a large YAML file which contains the following structure:

• CASE: ## should be "- CASE"
  ACCESSION:
  ...
  TXD_CASE:
  NICKNAME: ## next level/block of data but not a sequence (indent lost with formatting)
  ...
  SCRIPT_STRUCTS:
  - SCRIPT_STRUCT:
  RX:
  SUBSCRIPT_STRUCTS:
  - SUBSCRO{T_STRUCT:
  RY:
  ....

My issue is that using the representational model, I can get a list of the first level nodes under CASE but I don't know how to get to the the nodes underneath TXD_CASE: which is not followed with a sequence but if it were, then I wouldn't have a problem.
I believe that it must know about the substructure as it picks up other first level nodes listed after that TXD_CASE block.

I tried treating it as a sequence node but it complained that it couldn't cast the node into a Sequence node.
YamlSequenceNode txdItems = (YamlSequenceNode)mapping.Children[new YamlScalarNode("TXD_CASE")];

I am sure it must be trivial but I have not uncovered the trick!
Thanks, in advance, for your help.

[dlmcshan]

So, while I am pretty sure (but haven't consulted the YAML specifications) the YAML syntax is legit, I have a work around which is to modify the node following the TXD_CASE: (in my example) with "- NICKNAME" turning the TXD_CASE into a sequence node (even if it will be a sequence of one). I have about 50,000 such files so I will write a program to apply this fix to those files, assuming an immediate fix is not forthcoming.