What is the primary reason you want your child to learn English? Is it to provide them with the best skills to seek a job later on in life? To be able to obtain several degrees? Or perhaps to be able to communicate with as many different people as possible, to become a citizen of the world, to travel and explore, to be able to attend universities around the world and so much more. It is very common to wonder when your child is going to get a certificate they can use to verify their ability to use the language. Unfortunately it is not uncommon to hold several English Language degrees and yet have no ability or interest to converse at a basic level, perform simple tasks in English, etc.
Learning English can be fun, enjoyable and rewarding. Being able to understand the language, use it in different contexts, read and write using the correct grammar and spelling will allow you to acquire any degree given the right preparation. Again it is not a matter of when, as it is of how and why.