I don't have kids but find it absurd that parents who post photos of their kids online, be it them crying or smiling, don't put a single thought into the issue surrounding consent. Instagram photos aren't the same as my dad pulling out photo of his kids out of his wallet to show a coworker. They're permanent and will likely never disappear from the internet. And it's highly likely that these parents are posting hundreds of photos a year, so by the time these children are 28, they will literally have snapshots of their entire existence for the world to see.
I don't want to sound like "but think of the children", but seriously, think of the children...