No doubt that the policeman(s) might think that a small boy might be frightened and he will speak of the truth if he is felt threatened. I don't see the reasoning for them to point a revolver at the small boy irrespective of whether the revolver was loaded or unloaded. It does not matter. It is a threat and it is an act of oppression!!! Such an abusive should not be tolerated in the country.
Under the UK jurisdiction, PACE Act 1984 was designed to list out the many things which a policeman/ woman can do and what can they not do. I am no quite sure about Malaysian law but I do believe such act, upon successful investigation that if the claims are true, the policeman should be disciplined.