Do you understand English, both written and oral? How far is your level in mastering English? If you do not already know it, you better check by taking the English proficiency test http://britishlifeskills.com. There are many places to follow, one of the websites that provide information on special English proficiency tests for those wishing to continue their life in London is http://britishlifeskills.com.
Some of you may come from a country that does not speak English as the primary language. Since when did you know English? Whether as a child or as an adult? Keep in mind, age affects a person’s speed in receiving lessons. Children are usually easier to memorize and understand new vocabulary, let alone about language.
So, it never hurts to introduce English early on. There are many schools that use English as a daily conversation. If your child has some English vocabulary, they are more receptive when taught in school. You also have no trouble to teach them.