We want to be able to search across a parent/child relationship simultaneously, lets say fields 1-3 in the document below.

{
   "field1": "abc",
   "children": [
      { "field2": "def" },
      { "field3": "geh" },
   }
}

I see how this can be done with nesting, but there is the issue of returning too many children. or having to split the document as you suggest. If I separate children into a separate collection, and join them to the parent, I don't see a way to search across both collections at once based on the current specs for joins. But maybe I'm wrong there. Do you see a solution with joining?