Hello Nhien, welcome to the WritingPage, thank you for your contribution!
In general, your essay had described the problems clearly and briefly. Good points! Just some minor mistakes that I found out and would like to give you some suggestions! ;D
On the one hand, it is easy to understand why some people think that teaching the foreign languages for young children has some disadvantages. Firstly, the young children could be confused when they use language in their living. For example, they could not speak fluently the native language and this could affect to their communicating ability. An (no space) other reason that they ( the children) could use mixed words when they were talking with everybody. If the children do that, the others who do not know the foreign language could feel annoyed, and sometimes lead to misunderstand which should not occur.
However, there are certain benefits of learning the foreign language of grade-schoolers. One reason is that they have study and mimic ability very quickly(rephrase: they have the ability to understand and mimic very quickly) Teachers could associate this subject with playing GAMES
for their students. Moreover, pupils only start learning with basic knowledge such as simple vocabularies or sentences, this is not negative impact (rephrase: this will not impact negatively) on the learning of the other subjects. If parents worry about the using ability of native language of their children, limiting time of learning foreign language is the best way. In addition, when grade-schoolers come to secondary school, they will not have to spend much time to learn basic knowledge of the other languages that they could study more advanced learning.
In conclusion, it is undeniable we cannot deny (if you wanna use undeniable, it should be like: it is undeniable that the advantages of....outweigh the drawback of it) the advantages of learning the foreign language at elementary school and the educationalists should encourage to teach this subject for young children.