You are misunderstanding the rules, samsung.
For the purposes of FLR, the law defines a 'dependent child' as a child of the applicant or the applicant’s partner who is:
1) under the age of 18 years, or who was under the age of 18 years when they were first granted entry under family route;
2) applying for leave as a dependant of the applicant or the applicant’s partner, or is in the UK with leave as their dependant;
3) not a British Citizen or settled in the UK; and
4) not an EEA national with a right to be admitted to or reside in the UK under the Immigration (EEA) Regulations 2016.
So those children who come under 3) or 4) above are not counted as dependants in this respect as they are not applying for LTR and thus not counted for the purposes of calculating the appropriate financial requirement.