As a rule, children learn their native languages easily, including bilingual children. What's hard for adult learners simply isn't hard for children.

In this case, yes, the relationship between the two languages is 1-to-2, but that's true of so many things, it's just a normal part of bilingualism. Consider the English pronouns he-she-it and Spanish él-ella, which is a 3-to-2 relation and split up differently. Or how there are more forms of verbs in Spanish than in English, or specifically two aspectual distinctions in the past tense (one is punctual, and one is prolonged duration, but both are past tense, like the English past, though that's not split).

On the other hand, there has been so much research on this topic regarding second language acquisition there is probably some experimental or observational research on children too, as a baseline. I haven't specifically looked into it, but I'd assume you can find it out there.

For introductory level textbooks in Historical Linguistics, here are some good options:

Lyle Campbell, Historical Linguistics: An Introduction
https://mitpress.mit.edu/books/historical-linguistics-fourth-edition

Hans Henrich Hock & Brian D. Joseph, Language History, Language Change, and Language Relationship: An Introduction to Historical and Comparative Linguistics
https://doi.org/10.1515/9783110613285

Longer, graduate-level version:
Hans Henrich Hock, Principles of Historical Linguistics
https://doi.org/10.1515/9783110746440

Tore Janson, The History of Languages: An Introduction 2012, Oxford.


Each of those books has several editions. The older edition of Janson's book was called Speak but it's substantially similar content if you find a copy of that instead.

Campbell is a popular textbook, while Hock & Joseph is somewhat more comprehensive but still accessible to undergraduates, and Hock's graduate-level textbook is a dense and extremely thorough introduction that would cover just about everything you'd want to know starting out if you want to dive right into the deep end of the topic. These all cover sound change and other topics.

Janson is a different kind of introduction, and not very technical at all, also not really covering sound change. But I would recommend it (probably in addition to one of the others), because it's a very interesting read. It really talks about the history of languages, rather than historical linguistics in a narrow sense, and it takes a sociolinguistic perspective on how languages change through contact. It's a very accessible book to read for non-experts, but also interesting enough to keep the attention of experts, so it's a unique kind of non-technical but useful book.

One more I might add to the list, on a more specific topic:



David W. Anthony, The Horse, the Wheel, and Language: How Bronze-Age Riders from the Eurasian Steppes Shaped the Modern World
https://press.princeton.edu/books/paperback/9780691148182/the-horse-the-wheel-and-language
https://en.wikipedia.org/wiki/The_Horse,_the_Wheel,_and_Language

That one is about a specific topic, from an anthropological perspective on the history and spread of the Indo-European languages. It's well regarded by linguists, and also generally accessible to a non-specialist audience.

There are a lot of other interesting things to read, but that's a reasonable start. Some fun things to consider beyond this, but still with some relevance to familiarizing yourself with these topics, you might take a look at:

Edward Vajda, "J.R.R. Tolkien's imaginary languages" (YouTube lecture)
https://youtu.be/5NKlr0vRX34
(A fun and surprisingly relevant discussion of historical linguistics applied to Lord of the Rings. Tolkien was originally a philologist, and only secondarily an author! LOTR was in some sense based initially around the fictional languages he had created as a story and world to hold them.)

A bit more of a tangent, and not so strictly academic, but again fun for thinking about these topics:
https://conlangingfilm.com/
(A really well made documentary about conlangs)

David J. Peterson, The Art of Language Invention
https://artoflanguageinvention.com/books/

I mention those not because they are directly about historical linguistics per se, but because they bring up a number of related topics that might help make them more accessible to you from a non-technical perspective, but tying into the same questions we ask about language structure and how those structures change. One of the best ways to make a conlang is to "evolve" it from an earlier stage into the final form you choose, and that means applying the principles of historical linguistics. Peterson in particular is serious about making naturalistic conlangs through this process, and he has been successful in that of course, if you've seen his work in Game of Thrones and other movies and TV.

Daryl Zero: A few words here about following people. People know they're being followed when they turn around and see someone following them. They can't tell they're being followed if you get there first.

Daryl Zero: Passion is the enemy of precision. Forget the misnomer 'crime of passion'. All crime is passionate. It's passion that moves the criminal to act, to disrupt the static inertia of morality. The client's passion for this dead woman had facilitated his downfall. And the blackmailer's passion will facilitate hers. When you live with no passion at all, other people's passion come into glaring relief.

Daryl Zero: I can't possibly overstate the importance of good research. Everyone goes through life dropping crumbs. If you can recognize the crumbs, you can trace a path all the way back from your death certificate to the dinner and a movie that resulted in you in the first place. But research is an art, not a science, because anyone who knows what they're doing can find the crumbs, the wheres, whats, and whos. The art is in the whys: the ability to read between the crumbs, not to mix metaphors. For every event, there is a cause and effect. For every crime, a motive. And for every motive, a passion. The art of research is the ability to look at the details, and see the passion.

Yes, that makes sense, and there are other parallels in English like "let it be known".

There are various things that might be denied. One is that humans have a symbolic system for categorizing speech. I take that to not be reasonably deniable, however I believe that certain phoneticians adhere(d) to a non-categorial analysis of speech recognition.
Another that can be denied is the specific package-deal "phoneme" as contrasted with allophone with all of that biuniqueness stuff. I do deny that there is such a thing as a "phoneme", where /t/ is a phoneme of English and [tʰ t̚ ɾ] are allophones. It is true that [tʰ] can be derived by rule from /t/, but that doesn't justify creating a special theoretical category. There is a difficult question as to which structures exist in the phonological component and which only exist in the phonetic component, and for example there is good evidence that "nasal vowels" are not a phonological category of English, they are the result of phonetic implementation: but the flap is clearly a phonological entity.

A further question is what kind of thing a "phoneme" is. Is it part of phonological grammar, phonetic grammar, or something on the periphery of language, at the auditory interface with phonetics? The "speaker awareness" test is, indeed, not reliable exactly because speakers need specific training in their writing system, and they do not learn a general skill about "phonemes" from one language that can be translated to other languages. E.g. a speaker of Logoori may know how to write English and Swahili, and even Logoori but the writing system is defective in not representing all of the phonemes. Unless one engages a speaker in training in linguistics, the standard reaction to a vowel-quality, vowel-length or tone minimal pair is that "they are spelled the same". You can experimentally get them to identify words, but they don't have any awareness of what's a "phoneme" in their language.