Unmarshalling Hierarchical JSON in SQL Server 2016+
In this case, I'd use a cross apply.

DECLARE @json NVARCHAR(MAX) = N'{"menu": {
    "header": "SVG Viewer",
    "items": [
        {"id": "Open"},
        {"id": "OpenNew", "label": "Open New"},
        null,
        {"id": "ZoomIn", "label": "Zoom In"},
        {"id": "ZoomOut", "label": "Zoom Out"},
        {"id": "OriginalView", "label": "Original View"},
        null,
        {"id": "Quality"},
        {"id": "Pause"},
        {"id": "Mute"},
        null,
        {"id": "Find", "label": "Find..."},
        {"id": "FindAgain", "label": "Find Again"},
        {"id": "Copy"},
        {"id": "CopyAgain", "label": "Copy Again"},
        {"id": "CopySVG", "label": "Copy SVG"},
        {"id": "ViewSVG", "label": "View SVG"},
        {"id": "ViewSource", "label": "View Source"},
        {"id": "SaveAs", "label": "Save As"},
        null,
        {"id": "Help"},
        {"id": "About", "label": "About Adobe CVG Viewer..."}
    ]
}}
'

  SELECT 
     JSON_VALUE(a.value, '$.header') AS MenuItem
    , JSON_VALUE(b.value, '$.id') AS Id
    , JSON_VALUE(b.value, '$.label') AS Label
  FROM OPENJSON(@json) a 
    CROSS APPLY OPENJSON(a.value, '$.items') b