The Ica stones are definitely a hoax. I believe Erich von Däniken was taken in by them.
As for the Acámbaro figures in Mexico, thousands were made, but for a hoax? Possibly an expensive hoax as someone must have paid and took lots of time to make and fire them.
I believe I first read of them in a book by Erle Stanley Gardner of Perry Mason fame. He loved to travel in Mexico and find strange things. Only books of his I’ve read were about the Deserts of the SW and Mexico.
It’s in that article at the link.