On mobile, the Forums are not in the apps but in a browser, too. Since the forums aren't coded in Flash, there might be no difference.
I'm on a PC, Win7, Firefox.
Today, I tried the "children" function. This means to delete replies, "children" to a message.
Strange things happen.
When deleting the OP of a thread, the "children" function is not offered. It says that the whole thread will be deleted, and it worked.
I tried another "last posting", w/o children, and this time, it worked.
Deleting a message with it's child - worked.
No technical bug from my POV. I was uncomfortable though, since I don't usually censor my folks. Only once, after a public warning, have I deleted some expletive, but transparently, by editing the text. The members were not amused!