https://www.freemovement.org.uk/how-to-apply-for-a-visa-as-the-parent-of-a-child-in-the-uk/
So I just found this which would suggest that the parent route is not an option as we're still in a relationship, although we don't live together:
As stated in the Home Office guidance on this visa:
The parent route is not for couples with a child who are in a continuing genuine and subsisting partner relationship together. Applicants in this position must apply under the partner route where, or when, they are eligible to do so, or under the private life route. An applicant cannot apply under the parent route if they are or will be eligible to apply under the partner route,
So does that mean we'd have to all go together to the UK, and if so, I have to remain in the UK?