For those who are not aware of the difference between alphabets and languages, here is a short explanation.
A language is a structured system of communication. Hindi is one of the languages of India. A script, or lipi, is a writing system for symbolic depiction of a language. When we see a document, we can see what script it is written in.
अ आ इ ई उ ऊ
The letters above belong to the Devanagari script (which in turn belongs to the Brahmic lipi or writing system) , which is used to write Hindi and some other languages.
If you see the image text below, you can immediately recognize it as Devanagari script. If you don't know Hindi, then you are likely to think it is Hindi. However, it is a Marathi language text written using the Devanagari script.
An alphabet is a standardized collection of such symbols, each of which depict a phoneme (or a distinct unit of sound), arranged in a certain fixed order. For example, the Latin/Roman Alphabet that goes A, B, C, D, etc. It is used to write English and many other languages of the world.
The letters of Hindi are called varnamala which is not a true alphabet, but an abugida. Abugida means, the consonant letter is primarily important, and a secondary vowel notation (matra) makes one consonant–vowel unit (varna).
The abugida script uses sequences of such consonant–vowel units. For example, 4 varnas or consonant–vowel units
भा र ती य = भ् + आ + र् + अ + त् + ई + य् + अ
make the word भारतीय, where the consonants भ् , र् , त् , य् have secondary symbols to depict the vowels joined into each of them.
In contrast, the Latin alphabet has symbols or graphemes (in this case letters) that represent both vowels and consonants and a sequence of these make a word: I N D I A - here the vowels have the same importance as the consonants.
Hope this short explanation will help you to understand how to separate the concept of written letters and alphabets from spoken languages. This is relevant to understanding that spoken language must be learned first by a child, and the script can be learnt later. The spoken sounds of a language, the grammar, the vocabulary and the written letters are different aspects of a language, and it is more effective to teach a second language to a child the same way natural native language development happens in the developing brain of a child.