Family visa, PR or citizenship for the child born outside the UK?

Dear all,

My current situation is:

a) My son was born outside UK in Oct 2014, when I was holding Tier2 visa .
b) I got permanent residency in Sep 2016 and citizenship in Mar 2018.
c) I divorced in May 2017 and became the only custodial parent of my son via the court order outside UK.
d) My son is still living outside UK and being looked after by my parents.
e) However, my mom is ill now and cannot take care of my son anymore, so I need to bring him to UK.

How can I prove that I take the sole responsibility for my son? Should I apply for the family visa, permanent residency or citizenship for my son?

Many thanks for your help.

Philip

See similar.

Apply as a child.