English is so complicated that we teach it to kids.
I agree with you that English isn't an excessively complicated language, but this point is a rather moot one.
If you are referencing the teaching of English to babies as their first language, then it's irrelevant, as every language that is taught as a first language has been taught simply to babies. Babies learn their parents language easily, and there's some evidence that they even start learning within the womb, at least recognising the pitch patterns spoken around them.
A baby doesn't find learning their parents language easy or difficult, and as such can learn any language with ease. I'm pretty sure there have even been some children who were taught fictional languages (like Klingon) as their first language.
If you meant teaching it to kids though, as a second language, this is also not a fair point.
Children are significantly better at learning second languages than young-adults and adults. Even the most complicated language would be easier to teach to a child than it would be to a mature adult. The complexity of a language doesn't change whether we teach it to children or not, hence there are children who learn things like Latin, Ancient Greek, as well as modern foreign languages, like French, Spanish, Mandarin and Japanese.
And if you meant teaching it to kids, as in English lessons within English-speaking countries, that's not really teaching a language.
That's teaching advanced vocabulary and grammar, but is also significantly about teaching different means of writing, such as poetry and prose, and oratory and other oral skills. Things which aren't strictly necessary to have learnt the language. If you were a French-born French-speaking child in France, you'd be having French lessons with the same emphasis, but you'd already be fluent in French.
If you're going to compare the ease of learning a language then you should have to compare it from the standpoint of an adult person, learning it as a second language (and without having learnt any similar languages, such as a French-speaker learning Spanish).
English is the global language.
The majority of international communication is in English.
It is also the mostly widely spoken language by number of countries, being spoken as an official language by 67 different nations. Furthermore, it's the recognised official language of the Commonwealth of Nations, and is recognised as an official language of the United Nations and the European Union (which is of note given that Ireland, Malta and the United Kingdom are the only 3 nations in Europe that officially speak English).
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