No. The school’s decision does not establish the child’s immigration category, relationship eligibility or admissibility. Assess the actual family application separately.
Use the school letter for its proper purpose
The published joining-family description includes the eligible spouse and unmarried children under 21. Educational acceptance does not expand that group or make the principal’s application automatically successful. Ask the two questions in the right order and the confusion disappears.
First: is the child within the published joining-family description — an eligible spouse or an unmarried child under 21? Second, and only once the first has an answer: what does the school require, and by when? Asking them the other way round is what produces a family plan built on an enrollment letter.
The school’s decision speaks to academic admission and to nothing else; it establishes neither the child’s immigration category, nor the relationship, nor admissibility, and no school can widen a published family definition. Where the child’s age sits close to the limit or has changed during processing, have any applicable statutory age-protection rules assessed individually before anyone concludes either that the child qualifies or that they have aged out. A birthday is a fact, not the whole analysis.
The published joining-family description covers the eligible spouse and unmarried children under 21, and it is that description, not the school’s roll, which decides who can be included in the initial application.