I really don't know what people expect FAs to do with other peoples children.
I mean, FAs are not there to baby sit... although Im pretty sure they babysit a lot of the adults... but when people say the "FAs didn't do anything", what do they expect? Its not like an upset child is going to be receptive to a complete stranger swooping in, picking them up, telling them to shush and the kid will stop crying/calm down.
And then theres the parents that complain about the FAs not "helping". Again, FAs are not there to babysit your kids so what do they actually expect from the FA?
Kids usually cry for a reason, we may not understand or appreciate their reason but its how they communicate so unless its a out of control kiddie due to bad parenting there is no point to giving snide looks at the parent for being unable to shut their kid up because Im pretty sure most parents would love their child to have a happy, quite flight.