home.json.twig

{% set items = [] %}
{% for child in page.collection() %}
    {% set items = items|merge([{ frontmatter: child.header, content: child.content} ]) %}
{% endfor %}

{% set payload = {
    name: page.header.title,
    route: page.route,
    type: page.template,
    items: items,
    content: {
        body: page.content
    }
} %}

{{ payload|json_encode|raw }}

output.json

{
  "name": "Home",
  "route": "/",
  "type": "home",
  "items": [
    {"frontmatter": {"title": "Foobar"}, "content": ""},
    {"frontmatter": {"title": "Foobar"}, "content": ""},
    {"frontmatter": {"title": "Title 1"}, "content": ""},
    {"frontmatter": {"title": "Title 2"}, "content": ""}
  ],
  "content": {
    "body": "<p>Content stuff here</p>"
  }
}