API parameter to "include" resolving ids to objects

I have a NoSQL repository with two tables, Foo and Bar. Each Foo has some metadata and a list of Bar ids. Each Bar has some metadata.

I'm writing the API for retrieving a Foo and would like to provide the ability to specify whether the returned Foo contains either the related Bar ids or the related Bar objects.

For example, one could GET /foo/foo-id-1?resolve=false and receive the response

{
  "id": "foo-id-1",
  "metadata": {...},
  "bars": ["bar-id-1", "bar-id-2", ...]
}

Versus GET /foo/foo-id-1?resolve=true and receiving

{
  "id": "foo-id-1",
  "metadata": {...},
  "bars": [
    {
      "bar-id-1",
      "metadata": {}
    },
    {
      "bar-id-2",
      "metadata": {}
    }, ...
  ]
}

I'd like to do this because

1. In the case that the client only needs the Foo metadata and not the Bar metadata, I can save a call to the repository to retrieve the Bar metadata.
2. In the case that the client needs the Bar metadata included with the Foo, I can save the client a call by resolving the Bar ids to objects.

My questions are

1. What should be the name of the parameter that provides this ability? I've named it "resolve" but is there something better (perhaps "projection") or a standard?
2. Should the parameter be a flag, as I've suggested in the example above, or a string in case later more Foo children are added? For example, /foo/foo-id-1?resolve=bars,bazs.
3. Is it ok to have an endpoint (GET on /foo:id) that returns two different data schemas? That is, in the first case the data schema contains bars :: [String] and in the second bars :: [Bar]