Thanks for this essay and welcome to Writefix!
I think your attitude is really great. Your comment is written very well: some people think good writing stops at the end of the essay!
Your essay has three paragraphs, is 193 words long, and has an average 19 words per sentence (see http://www.read-able.com/). It's very important to meet the 250-word limit as you will lose a lot of marks in IELTS for writing fewer than this.
Develop your ideas
I really recommend an average sentence length of 12 words or so, not 19. Just make sure that you only have one idea per sentence. For example, this is 32 words long and has a lot of undeveloped ideas:
To start with, because they are still young so they can easily get new things and when they study about technology, biology, chemistry, physics…, they are getting more information and accumulate knowledge.
It's better to break the ideas into separate, shorter sentences AND to develop each one further.
Young people seem to absorb information more quickly than older people. Because of this, they can be exposed to a large number of different subjects at the same time without harming the learning process. Another point is that different kinds of subjects encourage different types of learning. Studying technology, biology, chemistry, and physics will develop their logical thinking and attention to detail. In contrast, subjects such as art and music will improve their confidence and spur their creativity.
Topic Sentence/Main idea:
I enjoyed the topic sentence in your second paragraph:
The reason why children have to learn so many subjects is that its necessary.
It's definitely a clear opinion, and Task 2 in IELTS is all about opinions! However, it might help you to reach 250 words if you gave some ideas on the other side, not just one side. Why might fewer subjects help some children? What might some advantages be? Even if you don't believe these advantages, give them in your essay and then demolish these arguments.
Try and avoid the words "things" or "stuff" from now on. They are lazy words in writing!
In the introductory sentence:
they also do not want their children to study to much necessary subjects.
Did you mean…?
they also do not want their children to study too many unnecessary subjects.
In the introduction sentence
Education for children is always the worrying of parents.
I might change to:
Parents always worry about their children's education. OR
Education is always a worry for parents.
Overall, it's a very good start and I think you have some excellent writing skills. Your essay is easy to read and moves nicely. Just develop your ideas, keep them separate, keep sentences short, and either mention both sides or give more examples of one side.
Looking forward to seeing more from you here!