LThomas777

If this is your MIL, then it is your wife who needs to speak with her. You both need to maintain a united front, but ultimately, she should take her mom out for breakfast and be respectful, yet honest. She can preface it by saying that you all love that she is involved with her grandchild and you value the time it gives you as a couple, but that there are some basic expectations you have as the parents. Those things include limited screen time (maybe you offer to provide activities/crafts when they are spending time together), a balanced diet (treats are fine, in moderation), and especially that your child attend school when he is healthy, regardless of if he is at her house or not. School is a priority and setting him up for success will involve everyone demonstrating that it’s important.
The bottom line here is that if you and your wife both feel strongly about this, it’s up to you as a couple to decide on the boundaries, but then it’s up to HER to speak to her mom about them while you play the support role. If this were your own mom, it would be up to you.
I’m sure she will put up a fuss and get upset, or say she isn’t going to watch your son…your wife needs to be prepared for that and meet it with a calm and confident “I’m sorry you feel that way. I hope you’ll change your mind, because he will miss spending that time with his grandma.” Then leave it up to her to take some space and recognize what she’s missing.