Thank u so muchI always believe in going with the guidance given by them in order to avoid problems.
If they clearly stated you need to inform any changes that happened after ITA, if I were in your shoes, I would do so in order to avoid any possibility of misrepresentation. There`s no way to hide a baby in the landing. If the baby isn`t in the files you`ll need to give a good legal reason for that when the official asks.
Best of luck with your landing!