One traveller said the feature let him know where babies "plan to scream... during a 13-hour trip".
Japan Airlines' website says the icon "lets other passengers know a child may be sitting there".
"I had three screaming babies next to me on my [New York to Doha] flight two weeks ago," he added.
"If you're not happy with a screaming child in the cabin, then I am more than happy [for] you to try and reason with them."
Please take note, @qatarairways: I had 3 screaming babies next to me on my JFK-DOH flight two weeks ago.