Here's a MIL story 
Recently been camping together with the grandparents. Every time the kids called me by saying "mum", she answered them "yes dear". MIL offers her opinion on how "her kids" - meaning mine, should grow up. These are examples of the way she references them.
I ignore all this as she is only person who babysits for me, as i dont have any other family. She doesnt look after them often, maybe one night a month. On the phone she asks after them by calling them "my kids". I find it worrying but dont rock the boat as i am happy kids have some family as i dont have my parents. I also dont like being petty.
Whats your thoughts?