While I don't have a definitive answer to this question, I am spelling out the issues latent in the question so it is clear to anyone reading it or looking for cases on point what is really going on in the question.
The Indian crime of instigation of abetment is what most U.S. jurisdictions would call solicitation to commit a crime.
let's say if someone impressionable (like a child or insane person)
does something as a result of instigation and encouragement would that
qualify as an act done in consequence of the abetment?
The general rule is that is you ask or direct someone to commit a crime, and they commit that crime, you are guilty of instigation of abetment of that crime with the same punishment as committing the crime yourself.
This rule clearly applies when the child or mentally ill person is capable of being guilty of the crime. There is no reason for it not to apply.
The hard question is whether you can be guilty of abetment of a crime that the person who carries out the acts that would otherwise constitute the crime lacks the mental capacity or age to be guilty of the crime due to insufficient age or insanity or a lack of cognitive ability to form the necessary intent to commit the crime.
Are you absolved of a crime that you knew was a crime, because the pawn you directed to carry it out lacked the ability to know what they were doing was wrong?
For example, what if you ask your three year old to shoot the nice lady at the front door in the head with a gun, and the three year old, not realizing what that means, goes ahead and does it. Are you guilty of abetment by instigating of the crime of shooting the women that the three year old child shot?
The answer clearly should be "yes."
You should be guilty of abetment by instigating a crime if the person you directed or encouraged to commit a crime did something that would be a crime, if you had done what you directed or encouraged them to do, even if the person who carried out your direction would never be someone who could be found guilty of that due to young age or an insanity defense or some other inability to have the necessary intent.
But, I don't have access to case law or legal authorities to confirm that conclusion under this statute in India. I'm sure that there is a case on point somewhere, however.