If you are native speaker of any language different from English, the greatest educational life hack is to learn English at the earliest time. It opens one's mind and allows access to content and communication at a global level.
Source: I’m a parent of a 3yo who now understands speaks both English and Polish. Me and my wife are Polish and only I speak English. Apart from speaking we also use English audio in all TV content she watches and buy books that contains both English and Polish text.
Edit: as pointed out below I should’ve clarified that this applies when you live in a non-English country where your child does not have any other way to learn English (over here you can’t really learn English in schools - not enough hours, plus it starts way too late anyways).
If you are living in a place where people don't speak your mother tongue but English is spoken everywhere and is the main medium of education, don't do this. The kids will pick-up English anyway because they will be exposed to it for 8 hours daily at school but if you don't speak with them in your mother tongue, they will never pick it up. The older they get, the harder it is. First hand experience.
Bilingual children whose parents don’t speak the language of the community at home may learn languages slightly slower but they quickly catch up once they make friends who only speak X.
By the way, something nobody mentioned, once your kid learns English in an English speaking country, your English gets better (assuming you are non-native). My daughter started correcting my pronunciation and it's getting way better
Source: as a kid I was in that situation, at first my parent spoke only in English with me and I started to forget Portuguese. After my parents realized that they pivoted to speaking Portuguese. I learned English fine at school and never had problems with either languages. Now I'm a parent of a 2yo and 1yo and am speaking Portuguese with both.
If you live in an English speaking country then sure. Over here it’s almost impossible to learn English in school, you only get a few hours per week of English classes.
Looking back at it, after 3 decades, what helped me learn the language was that immersion I mentioned, i.e. I was watching English TV programs (Cartoon Network, Eurosport, MTV Europe) for a big part of the day, without that I wouldn’t have been able to pick it up so easily.
There is absolutely nothing going on in the world to suggest that happen in the foreseeable future though. There is no competition, and it's inherently hard to change like any standard due to chicken-and-egg, so it tends to only happen when the entire world system is completely upheaved, to the point of the old world being a small part of the new world, and to a degree far greater than the possibilities of today. The stuff going on in the world today is mild comparatively.
In particular, politcal falls of the sponsoring empire don't directly lead to much change here, actually. Latin kept being the language used throughout Europe centuries after the Roman state was gone and buried in the west. Scholars were still writing in Latin in the 1600s. Within my parents' lifetime, Catholic mass was still said in Latin.
Let's check back in 30 years, and see if we have to reply in Mandarin, Arabic, Russian, or Malbolge.
The world you are imagining could just as easily be one where Chinese and Arabs dominate, the US and UK are a joke, and yet the dominant coalition paradoxically speaks English at least for elite communication anyway.
Did you know the original Latin language came from a tribe called the Latins that were vanquished by the Romans?
Reading the history of English after the Norman Conquest might be instructive too. For centuries the common people spoke the language that had been spoken locally, while the elites spoke the language of the old conquerers.
Fundamentally, you underestimate the chicken and egg effects involved, and they happen on a time scale of generations because that's the time scale upon which people learn languages.
If you are learning English later in life, you will struggle.
English is probably one of the dead simplest languages of use to learn later in life.
My dad (who learned English as a second language after his native Spanish, and also learned Portuguese and Latin, don't recall if he knew any others) used to claim English was one of the easiest languages. I don't recall his reasoning but I think it might have been because the rules (other than spelling lol) were simple and forgiving.
And I've met people who felt the opposite. Idk.
Still doesn't hold a candle to Mandarin or Japanese, of course. These guys are just on a level of their own. :)
In purely intellectual terms, know thy enemy.
I always say English is what Esperanto wanted to be.
Most money is spent in manipulating English media. Only fractions for other languages. It makes a difference.