Anonymous wrote:
"Hello MIL, from now on we have decided to stop the candy train. Thank you so much for sending candy in the past. Please don't send any more."
"Hello MIL, thank you for the candy we received today. I got rid of it, since I told you we were not accepting candy anymore. I appreciate the thought, however."
"Hmm, what candy? Oh, I don't open your packages anymore now. They go straight in the trash."
And then she'll get it.
OP doesn't need to be cruel. The MIL is trying desperately to shower love on her grandchildren. There's a better way to handles this then "they go straight in the trash."