First, I am a grandmother of a 4 year and 5 month old and I do not stand in unison with your mom. She was wrong. My grandchildren are my son’s kids and if I had done that, I would have paid dearly. But you see the boundaries were set immediately. They are the parents and they alone make all the decisions. I ONLY offer advice, help, opinion, if I am asked.
Good luck and I am so sorry.