The Short Version
No source in the available evidence provides a Ba Đình District-specific count of children with disabilities. The 1,500–3,000 range is not drawn from any official survey, administrative record, or published estimate for the district. It appears to be an unsupported extrapolation from Hanoi-wide and national aggregate disability statistics, which cannot be validly disaggregated to a single district without district-level data that does not exist in the evidence pool.