public interface ChildRepository extends JpaRepository<B, Long> {

    @Modifying(clearAutomatically = true, flushAutomatically = true)
    @Query("""
        DELETE FROM B child
        WHERE child.parent.id = :parentId
          AND child.id IN :deleteIds
        """)
    int deleteByParentIdAndIds(
        @Param("parentId") Long parentId,
        @Param("deleteIds") Collection<Long> deleteIds
    );
}

@Transactional
public void deleteChildren(Long parentId, Collection<Long> deleteIds) {
    if (deleteIds == null || deleteIds.isEmpty()) {
        return;
    }

    if (!parentRepository.existsById(parentId)) {
        throw new EntityNotFoundException(
            "Parent not found: " + parentId
        );
    }

    int deletedCount = childRepository.deleteByParentIdAndIds(
        parentId,
        deleteIds
    );

    if (deletedCount != deleteIds.size()) {
        throw new IllegalArgumentException(
            "One or more child IDs do not belong to parent: " + parentId
        );
    }
}