How do we learn about emotions as children? How does a child know what is sadness/anger/joy/anxiety /frustration etc and how to react to those ?
In the beginning the only comunication we have is crying or smiling :)
frustration 
Babies cry for reasons besides hunger. They cry when they feel discomfort (messy diaper....feeling too cold/hot....when they are sick or feel pain...whey they feel scared...). Infants can learn their emotions from those around them. They're more observant than we give them credit for. They can (with time) sense mood changes in their parents. They experience feelings of loss and anxiety.......such as when you take a toy away from them......or when mommy/daddy disappear from their sight for a few moments....etc etc. They also tend to mirror the actions and responses of their caretakers. And I think that maybe some responses might be innate....such as smiling back at someone, etc.
As children grow older and they are able understand (with greater depth) a variety of situations and feelings from their own experiences and those around them.
LP, babies have emotions too. They smile when you look at them or play with them or touch their checks or talk to them. They cry when you fake being angry, etc. Have you not played with babies? So don't think babies don't have emotions.
I think they all are learned and offcourse they learn from their parents, i have seen how fast kids learn emotion from their parents its good to be happy all the time but sometimes you can?t control your anger and you kid learns so fast from you
Yes they cry when their diapers need to be changed! also they will let you know when they need to Burp!
they also cry if you leave them alone in a room! and some time that is the Loudest!
Naak behna is a emotion too. Very depth in there. Nobody understands it properly surh surh karing
Isi lye to Munawwar Zareef ne farmaiya hai..
Baby tu kitni bari hogai..
Sorry couldnt find the link
This means we are born with primary emotions and learn the secondary ones by observing others around us.
What if the people a child observes are messed up emotionally? Does the child learn the same?