One should know at least 3 languages to communicate well. Mother tongue, National language, International language.
Knowing language well doesn't means to just know basic speaking or writing. As per Mahatma Gandhi if you know 3 synonym of all words of particular language only then it can be considered that you that language well.
Language learning has many minute aspects from spelling corrections to sentence formation, From proper tense to correct word selection.
Every language has its own identity and uniqueness, and there is also difference between language and dialect so every such aspect has to been keenly taken care of, and this is absolutely not possible without complete guidance. A teacher, a knowledgeable head, a language perfectionist shall hold command of making your child speak correct, Write correct, communicate correct. Verbal communication needs a lot of precision hence one can't compromise over language.
Here, reliable language head shall teach kid about language and guide them towards hold better command over language. One must know the language to know the world!