I can’t find reference in primary science guide that P6 needs to learn gravitatiional force. F=mg (m is mass of object and g is gravitational acceleration, constant, for free falling object) . So for falling objects of same mass, downward gravitational force is the same.
The question is likely a trick question to confuse a student between
(1) graviational potential energy (more for the boy A)-in syllabus and
(2) gravitational force (same for both boy).
If concept of g is not required, then this question is invalid to test a P6 student. Can consider double check with school science teacher. good if you can let us know here any outcome or reference point. Thanks.