When I was in uni my housemates had a baby, and we taught them some sign language so they could communicate before all their mouth parts were coordinated yet. None of us knew Auslan but two of us were familiar with the signs that the State Emergency Services used in the field so we worked with those.
The kid learned to request a drink, which is great, because that's like the #1 most important thing for a baby to be able to request, but instead of learning any of the other signs they just used modified versions of the drink sign to ask for all kinds of things. They couldn't actually make the proper drink sign (it requires some level of hand control) and used a modified wave, so they ended up with a whole bunch of subtly different waves to ask for stuff. Which was pretty fun in public because strangers would coo over this adorable baby who kept waving at them when, in practice, the baby wanted their ice cream.
Our kid used the "milk" sign for any and every liquid, including Lake Huron. We went to Mackinac when they were a toddler, they looked over the edge of the ferry and got so hyped up yelling "wa-juice! Wa-juice!" (Everything was either water or juice at this point in their life) and signing about it. Didn't know what to make of the waves.
My friend's baby also learned some simplified baby AUSLAN and he would sign GIVE at whatever he wanted. Your lunch. Passing birds. The book he just handed you. Just at you, when he wanted attention. The time he demanded *the wind* was perplexing.
I used to have a baby in my class who, any time we had a car go by the classroom window, would watch it go by and then look at me expectantly and start signing "more? more? more?" and pointing at the window. It was adorable, and sweet that he thought I was that powerful, but unfortunately I couldn't make more cars go by for him.
