Having it so your baby can ask for milk long before they get upset or too hungry is great, having them tell you that they're finished eating is much better than having them just throw food on the ground ;) Babies are cognitively capable of communicating they just haven't developed the skills for speech yet.
This! We started baby sign and could communicate these basics with our daughter before she was a year old. It might not sound like much to start communicating 6 months earlier, but I can only describe it thusly: awesome.
It's a popular trend because kids are able to do sign language before they're able to speak. IIRC it doesn't seem to help their language acquisition or cognitive develop at all, but it doesn't seem to hurt much either.
I've heard that it can lead to less frustration when the child has a means to communicate with the parents. If they know enough to be able to sign their brains are developed enough to want to communicate something.
As a counter-point, my daughter did not pick up on sign language at all. The advice that we got was to stick with a single sign and keep at it until she signed it back at us. My wife chose "Milk," but that was probably a poor choice. I don't think that she recognized "Milk" as being an object until well after she was speaking. It wasn't until she started drinking non-breast milk that she started saying "milk."
Now she's 19 months old and the only sign language that she know is "more," but she has an great vocabulary. She can even say her own name and the names of all of her friends. (It's also really cute when she says 'zombie')
> I've heard that it can lead to less frustration when the
> child has a means to communicate with the parents.
Absolutely. Our youngest kids learned a small handful of signs (five or so) before they could speak, and it made things much easier. "More", "milk" (was hard to teach, but when it stuck it was great), "banana", and few others. Someone else here said "done" was useful, and I wish we would have done that one.
It's pretty common to teach children a little bit of sign language before they can talk, actually. I remember being really impressed that my niece was able to ask for more of something (generally food) using sign language long before she spoke her first word.
We're doing this with our second child now. It removes a lot of frustration from the parents and the kids when the child can actually communicate about what they want, see, hear, think, etc. It seems to cut down on fits, and definitely helps us communicate. As one of the other commenters said kids' language apparatus is fully functioning before they have the fine motor skills necessary to make all the speech sounds they need to say words, so it's a nice hack :) Teach them sign language which they have enough fine motor skills to use until their mouth control gets to the point that they can speak.
Our first kid is now 5 and doesn't really remember any signs, but he said sentences and told stories even in sign language before he could speak well.
> As one of the other commenters said kids' language apparatus is fully functioning before they have the fine motor skills necessary to make all the speech sounds they need to say words
To add to this: My son is 30 months, and his speech is coming along well, but one really fascinating part is how he will construct sentences that are far more elaborate than what he can say, and substitute "missing" words for with a specific sound.
It is clear these aren't "just" sounds from how he'll repeat phrases with the right number of "words", just some of them are padded out because he doesn't know how to say them yet, and then gradually more words will get added to the various phrases as he figures out how to pronounce them.
Children can usually learn to sign before they can learn to talk. My toddler had a vocabulary of about a dozen signs before he could say any useful words. It help relieve a lot of their frustration, and generally makes them happier when they can communicate.
We didn't teach our son signs on purpose, but he picked up some by himself before he could speak.
For example, we would point at a bottle of milk to see if he wanted some, and he would soon start copying our gesture by holding up one hand as if a bottle placed upright, and pointing at it with his other hand. Soon he would do that whenever he wanted milk, before he got thirsty enough to start crying.
A lot less guesswork for us, and a lot less crying for him.