Question: correct way to get children?

### Go Example
```go
package main

import (
"github.com/davecgh/go-spew/spew"
"github.com/hashicorp/hcl"
"github.com/hashicorp/hcl/hcl/ast"
)

func main() {
hclStr := []byte(`
a "b" "c" {
d = "e"
f "g" {
h = "i"
}
}
`)
objRoot, _ := hcl.ParseBytes(hclStr)
objList, _ := objRoot.Node.(*ast.ObjectList)
spew.Dump(objList.Filter("a", "b", "c"))
spew.Dump(objList.Filter("a", "b", "c").Children())
}
```

### Expected behavior
I would think it would return the nested `f` object.
What should have happened?

### Actual behavior
I get no objects/items returned.

### Steps to reproduce
1. run the example above