How to get children's children path?

Hello. I have a page which creates the gallery from child pages. Child pages have their child pages. I need to get children's child page path.

Example: portfolio page loads all from directory Graphics. Inside Graphics dir there is another dir: Cup.
I need to enter the Cup page from portfolio page by link.

---twig
{% for child in page.children %}
{% for a in child.children %}
{{ dump(a.route) }}
{% endfor %}
{% endfor %}