I am not a parent or a stepparent but it would seem to me making sure the older stepchild was not feeling displaced or different than the bio child would stop a thinking person from using that kind of wording.
I thought the picture was of her 18 month old daughter that said this is my real child. And I also noticed that she did not put Kyron up as her profile picture for several days. Kaine put his picture up immediately as well as a lot of their friends.