Why would your in-laws think their daughter- in-law is eating the candy they are gifting their grandchild? Do they not trust her to keep the food for her? Can't the kid share her treats with her family?
Some in-laws are very weird towards their daughters-in-law. As if they couldn't accept the person that their child married just because they are not biologically family. This always makes me think if the problem is whether they don't trust their child's ability to choose a decent and loving partner, or if it's just because it's an outsider to the family and they need to act defensively. Whatever the case is, it's not only malicious to be acting this way, especially if they are the mother of your grandchild. They are part of the family whether the in-laws like it or not, so it's better to get used to it instead of acting all weird and crazy. They married into your family; they didn't steal your child or push it away from you. They just fell in love and decided to form a family on their own. Isn't it easier to accept them into your family than to mistreat them all the time?
The grandparents in this story are not doing things right. They are being incredibly disrespectful by assuming that a mother would take a gift that was supposed to be for her daughter. Yes, it's just candy, but it's also so much more than that. If a mother takes candy from her daughter so she can eat it, what other wicked things does she do? The saying "taking candy from a baby" is the most well-known phrase to describe a witch, so do they think the mother is a witch? I think that these in-laws are either overthinking some little situation and creating a huge mess over it when it's nothing in reality, or they just saw the kid offer one of her candies to her mother and they took it the wrong way — which is insane to do.
I don't like this people's attitude, and I do think that if they do this big of a mess over something this dumb, then it's better to keep your distance from them. If this whole family drama started over some candy, what can happen with a bigger misunderstanding? I don't think that they like the mother of their grandchild in the first place; the way they acted all defensive over nothing proves it. I do think that the mother is right to be upset over this. After all, they are spreading lies about her, and even if they are dumb, no one wants people to be lying about them, especially to their family. I do hope that the husband stands up for her family and either makes his parents understand why they are wrong or at least forces them to change their attitude. No one deserves to be treated like this, and taking your distance seems like the best solution to avoid a bigger fight over nothing.