I knew two brothers that would mix words from different languages while speaking to each other because they shared the same set of languages and presumably used the best words to express their thoughts.
Your daughter probably knows other people generally speak and understand one language at a time and just conforms because its most effective.
I'm not sure if or at what age it might be good to start mixing languages with others who can.
Speaking to babies is incredibly important for linguistics but probably for all types of complex brain function, I don't think there is an upper bound on how many words we should expose children too.
That's downstream of the sponge phase. So much so, that initially we only absorb and don't talk yet.
It's an interesting hint at the deeper evolutionary origins of language in the ability to plan complex actions, providing a neural basis for the observation that language and action planning have this common structure of an overall goal that can be decomposed into a structure of subgoals, which we see formalized in computer programs too.
This is an older reference (1991) where I first heard about it. there are more recent studies reinforcing various aspects of it but I didn't find one that was as comprehensive
> The brain’s general object-recognition machinery is at the same level of abstractness as the language network. It’s not so different from some higher-level visual areas such as the inferotemporal cortex (opens a new tab) storing bits of object shapes, or the fusiform face area storing a basic face template.
In other words, it sounds like the brain may start with the same basic methods of pattern matching for many different contexts, but then different areas of the brain specialize in looking for patterns in specific contexts such as vision or language.
This seems to align with the research of Jenny Saffran, for example, who has studied how babies recognize language, arguing that this is largely statistical pattern matching.