Errors:  

- In today's modern world" is redundant; use "In today's world.

- try hard enough" could be more precise.

- I will discuss both the advantages and disadvantages of this message below" can be rephrased for clarity and formality.

Corrected version:

In today's world, some people say that it is very important to tell children that they can achieve anything if they work hard enough. I will discuss both the advantages and disadvantages of this message below.

Improved version:

In today's world, some believe it is crucial to tell children they can achieve anything if they work hard enough. I will explore both the advantages and disadvantages of this message.

Errors:  

- many advantages of this message" can be rephrased.

- aware about" should be "aware of".

- and they will succeed in their life" could be clearer.

Corrected version:

There are many advantages to this message. The primary advantage is that if parents and teachers convey this message to children, then children become aware of their aims and they start studying and working hard. This encouragement helps them to think about their future and they will succeed in their lives.

Improved version:

There are several advantages to this message. Primarily, if parents and teachers convey this message to children, they become aware of their goals and begin to study and work hard. This encouragement helps them focus on their future, increasing their chances of success.

Errors:  

- plenty of difficulties could be more formal.

- provide them with positive thoughts" could be more precise.

Corrected version:

Another reason is that some children face many difficulties in their lives and always want to achieve their goals but are unable to. In such cases, if teachers give them positive encouragement, it will help boost their confidence levels.

Improved version:

Additionally, some children face numerous challenges and struggle to achieve their goals. In such cases, positive encouragement from teachers can significantly boost their confidence levels.

Errors:  

- also some" is redundant; use "some".

- sometimes fall into depression" could be rephrased.

Corrected version:

On the other hand, there are some disadvantages to this message, such as family pressure, depression, and disappointment. If parents constantly repeat this message, children may become frustrated and fall into depression. If teachers always try to convince their students to achieve their goals and students try hard but are not able to achieve their goals, it can lead to disappointment.

Improved version:

On the other hand, there are some disadvantages to this message, such as family pressure, depression, and disappointment. If parents constantly repeat this message, children may become frustrated and fall into depression. Additionally, if teachers continuously push students to achieve their goals and students try hard but fail, it can lead to disappointment.

Errors: 

- we can say" is redundant.

- Sentence structure could be improved for clarity.

- confidence level" should be "confidence".

- tell this message" should be "convey this message.

Corrected version:

In conclusion, there are both disadvantages and advantages to this message; the advantages outweigh the disadvantages. This thought is important for children, especially for students, because it helps to build their confidence and encourages them to work hard. Parents and teachers should convey this message in a polite and supportive manner.

Improved version:

In conclusion, while there are both advantages and disadvantages to this message, the advantages outweigh the disadvantages. This belief is important for children, especially students, as it helps build their confidence and encourages them to work hard. Parents and teachers should convey this message in a polite and supportive manner.