For children under the age of 3, I've noticed that there are certain words that help with their communication development with adults on their needs and wants. It's obvious that a baby being able to say eat or milk is better than them crying and the parents guessing what they want.
What are some other useful words that every baby should learn to help with navigating their day to day environment?
I think you are not quite right in looking for words, I would look at what interactions you expect and aim to have a word or two to make that interaction go smoother. Consider what you want them to be able to report to you; saying cat, dog, bus, car, or uncle might be helpful things for them to be able to communicate to you in a morning routine. Most interactions initiated by the adult can be worked through repeated yes/no's without too much trouble.
The words that help my interaction with a toddler most (other than the nearly impossible to avoid no, up, and family names) are in order:
By 3 I would expect them to understand everything. They may not be comfortable making all the sounds yet, add probably aren't practiced using big words, but they probably have work-arounds for their trouble spots, like knowing to say "like a stop sign" if someone doesn't understand their pronunciation of "red".
I live in a cantonese speaking family house, I've noticed my 18 month old nephew use the following words very frequently vs just crying for what they want to communicate in other cousins I noticed.
These are the words I've noticed on a daily basis:
I realized that due to their still developing vocal cords, its easier for them to say 1 syllable phrases vs multi-syllables. In some languages, its easier to say certain things as long as its 1-2 syllables only. In chinese there are many one syllable words, as many of the words sound the same due to the nature of a tonal language ( https://simple.wikipedia.org/wiki/Tone_language ).
