Well, there is clearly a disparity in the story:
A Southwest Airlines flight attendant reportedly removed a baby from her parents' care mid-flight after witnessing the mother slap her crying child.
Vs:
"In this case, it was a baby that was upset, and the flight attendant asked the mother if she wanted help with the baby."
If it's the former, then it's absolutely none of that FA's business unless there is clearly an assault/abuse or a threat to the safe conduct of the flight.
Otherwise, it's none of their business.
I smell a lawsuit if it is, indeed, the former.