How do I approach my mother to talk to her about her blatant favoritism she shows towards one of my children?

I have a 3 yr old and a 1.5 yr old- both boys. My mom shows blatant favoritism to the oldest. At first it was okay because the baby was just a baby and we just chalked it up to the oldest being more interactive. But now the youngest is getting older and interactive and she still pays 1/4th the attention to him. My wife (rightly so I completely agree with her) doesn't want my parents watching the kids because of this. The youngest is getting to an age it will actually affect him. It is heartbreaking to me. How do I approach her about this? Frankly I want to just be straight forward- I guarantee she will deny it though. What do you think? via /r/Parenting http://ift.tt/2ahxzJ7