Suppose your kid steals a bag of chips from another kid and you want to make him/her understand that what he/she did was wrong.Now you go to the movie theatre and you are buying 2 bags of chips one for each of you.Is it ok to take your kid's bag of chips , eat it and then say to him/her "Did you like it?Do you think the kid you stole his/her bag of chips when you were at his/her house liked what you did to him/her?".What you did is cruel,but it made your kid get in the position of the other kid.However are there any reasons not to do this?
I find it very unlikely that this would cause the desired effect, and in fact might do harm. The reason I believe this wouldn't help is that the child-thief probably was able to imagine that the victim might feel bad about this; they most likely just didn't stop to ponder how their act might affect the victim. (Or, less likely ut worse they knew but didn't care.) By giving something to your child and then taking it away you are more likely to teach lessons like "My parent is sometimes cruel to me." or "It is to be expected that sometimes your stuff gets taken from you.". Neither lesson makes for a well-adjusted child.
Instead, support the thief in contemplating afterwards the impact of their actions, and assist them in reaching the conclusion that they owe the victim restitution (and assist them in figuring out appropriate restitution - probably giving snacks of slightly higher subjective value to the victim).
This response assumes the child does not understand the victim's point of view and ignores any other possible reason for the child's actions.
Instead, I would recommend a discussion with your kid in the format of Dr. Ross Green's Plan B method for debugging problematic behavior.
Would my behavior towards my child have the desired result?
If the desired result is for your child to not take other people's things, then modeling that undesirable behavior is unlikely to achieve that. It's possible they end up learning the exact opposite message. Because you're demonstrating that it's okay for you to take their things (since you did it despite knowing how they would feel), they may learn they can ignore how their victim will feel and do it anyway.
This method does not teach empathy but instead reinforces the idea that a victim is powerless. This can be dangerous because a child may decide that feeling powerless sucks and would rather continue being on the other side of the dynamic, e.g., continuing down the path of becoming a bully in order to avoid feeling powerless.
are there any reasons not to do this?
Yes. Children learn by what they see, but they also may act impulsively as children may not have yet developed impulse control (and in the case of neurological conditions like ADHD, it may develop much later or require medical intervention to manage it).
An alternative reason for the child's behavior could be as simple as they were hungry and the chips were there.
By modeling only the behavior you want them to mimic, you teach them how to handle themselves in similar situations.
By not figuring out what the real cause for the theft was and assuming it was for nefarious purposes, the child may internalize that they are bad and deserve bad things happening to them for seemingly no reason. They may also receive the message that @Arno pointed out and that, "my parents are sometimes cruel to me" which could undermine your position as their safe/comfort person. If this is a go-to parental response, then this could damage your relationship with the child where they don't feel safe coming to you with important things due to fear of you possibly responding in a cruel manner, regardless of the lesson you're trying to teach.