Maybe it was a well scripted con. Did the mother pay for her stuff?
Did you know the mother and child?
I grew up as a single child and I enjoy the happy noise of children.
It has happened that a screaming kid looks at me to see my reaction. I look back - how I look I do not know - but all of a sudden the kid just stop screaming and look ashamed.
Once a sneaky boy stuck his tongue at made nasty grimasses to me. As his mother looked the other way I did the same. His reaction was worth a good laugh.
There's also the possibility the child is autistic or has ADHD or a number of other options