First, stay away from expressions like "in my opinion." It's your essay; this is understood, increases word count, and takes time if the essay is in an exam situation.
Second, this is a topic with a GREAT DEAL of social science research. If you have an unlimited time frame, this is the sort of thing you can at least get as far as Wikipedia. Some of the data is conflicting. This can be part of your conclusion.
Third, a great outside-the-box argument would suggest an approach in which children don't require very much discipline or punishment because they've been given appropriate guidance. (I have kids.) Things like stability, structure, exercise, love, a voice in family decisions, lessons in charity and generosity and peaceful resolution of problems, safety, empathy, and compassion reduces discipline issues probably 80-90%.
Specific to your question, your introduction sounds like a conclusion. An introduction should define your question and clarify your end points (e.gs. this or that, this and that, or this or that or some other entity). In your sentence, it appears you are being on-topic and in agreement.
However, in consideration of above, I'd rewrite your sentence more simply: If punishment is necessary to educate children in the difference between right and wrong, it should be thought out, agreed upon by both partners, and proportional to the offense. Again, this sounds more like a conclusion rather than an introduction.