childCount property
You must ask the API to count children (with asTree=true&countChildren=true), otherwise this will be null. This will be the complete direct child count, whereas children may only contain a subset based on pagination.
Please note: This property should have been non-nullable! Since the specification file does not include a default value (using the "default:" property), however, the generated source code must fall back to having a nullable type. Consider adding a "default:" property in the specification file to hide this note.
Implementation
int? childCount;