One of our dc has a health condition which means that certain foods should be avoided. It's not a life or death situation like a nut allergy but still something serious and something that we are still learning about under direction of healthcare professionals.
I don't really want you to go into it because it would be quite identifying, but what I can say is that it's not just us being precious, and it's not difficult to avoid these foods or find alternatives.
Grandparents are fully aware of our dcs health and we have explained the consequences having these foods have on dc. We have made it crystal clear and have even handed things back when given as gifts and told them "dc cannot eat this". Despite this, they repeatedly ignore us and give these foods anyway when we are not there, but "just a little", or "we didn't think x or y was excluded" even though they damn well know.
I don't know how many more ways we can say it now.