Suggest to them some alternatives maybe, but the burden to cater to them shouldn't fall on you.
As a parent, I couldn't imagine doing that in response to a dinner invitation. I might ask what you were making to see if they would eat it, and if it wasn't something I thought they would eat I would come up with another solution myself. I wouldn't force the kids to eat food they didn't like - you have to do it sometimes but it kind of ruins the "enjoying dinner with friends".
I might feed them beforehand, or get a babysitter or something. Otherwise - I would just bring food for them myself (PB&J or something). When I'm going to visit a friend, I'm a guest in their home - not a customer in their restaurant.
As a parent, I couldn't imagine doing that in response to a dinner invitation. I might ask what you were making to see if they would eat it, and if it wasn't something I thought they would eat I would come up with another solution myself. I wouldn't force the kids to eat food they didn't like - you have to do it sometimes but it kind of ruins the "enjoying dinner with friends".
I might feed them beforehand, or get a babysitter or something. Otherwise - I would just bring food for them myself (PB&J or something). When I'm going to visit a friend, I'm a guest in their home - not a customer in their restaurant.