I am wondering if we are slightly at cross purposes;
Your reference to notary appears to be the lawyer in the other jurisdiction.
My reference is to a UK affidavit sworn with a UK Notary and then legalised via the Foreign Office by the UK Notary for use in the jurisdiction.
Affidavit citing parentage and Childrens Act, parental responsibility with registrar copy birth certificate attached – the UK Notary if necessary can usually arrange translation if required.
Children Act 1989
c. 41Part I
3 Meaning of “parental responsibility”.
(1)In this Act “parental responsibility” means all the rights, duties, powers, responsibilities and authority which by law a parent of a child has in relation to the child and his property.
(2)It also includes the rights, powers and duties which a guardian of the child’s estate (appointed, before the commencement of section 5, to act generally) would have had in relation to the child and his property.
(3)The rights referred to in subsection (2) include, in particular, the right of the guardian to receive or recover in his own name, for the benefit of the child, property of whatever description and wherever situated which the child is entitled to receive or recover.
I should imagine the UK Notary fees would be around £300 and the legalisation / delivery about the same or a little less.