When right-click -> Drop ... (or Shift + del) and confirm on a parent table that have child rows, by default HeidiSQL drops the table without checking foreign key constraints. I consider it appropriate to display a Turn off foreign key checks? checkbox in the confirmation dialog box, and that the default behavior is checks foreign key constraints (in other words, the checkbox should appear unchecked by default).
PS: Sorry for my English. It is not my native language.