EXPAT FAQ
https://www.easyexpat.com/en/faq.htm
Can I get a UK passport for UK born children
Your children are not entitled to dual citizenship unless one or both of the parents are actually UK citizens (the parent has to be a UK citizen OR domiciled in the UK).
According to the British Nationality Act 1981:
Under s.1(1), a person born in the United Kingdom on or after 1 January 1983 is a British citizen at birth if, at the time of the birth:
either parent is settled in the United Kingdom