Suzie said
all of the schools nearby...
native British are a majority. By native British, I am including second and third generation black and Asian British children
And in doing so you are creating a contradiction in terms.
We are speaking of the ethnicity of children in London schools, and if children are 'native British' by ethnicity , then, by default, they are not 'Asian British' or 'black British'.
You are choosing to misuse the description 'native' to designate only birthplace, and since you know that the discussion was about ethnicity of children in London schools, NOT whether they were British or foreign born, you are clearly deliberately trying to muddy the waters and divert the discussion.
If discussing the ethnicity of President Obama and President Trump you would not describe them as 'native Americans' based on their birthplace, that descriptive is reserved for those of indigenous American descent. Kindly accord the same respect to the indigenous people of Britain and other European countries.
So back to your observations about your local schools, I think we can safely conclude that the ethnic majority British i.e. native British, have already fallen to ethnic minority status in all your local schools. I am not surprised!