But, that's life, no? We can never make plans that work out all the time. I'd say, as a father of a 5 and 3yo myself, it's a great opportunity to demonstrate/teach the kiddos how to deal with those situations.
The point of days like that, and what I highlighted to my oldest when we had a similar disappointing outing this weekend (we all wanted to grill in a park, packed everything up, but forgot it was Easter and every other family had the same idea and we were screwed), is that we still get to have a nice time with family one way or another, regardless of what we're eating.
It's definitely disappointing when time is super limited, I completely empathize! I guess I just always try and highlight the glass half full aspect of things and use that to find a way to make the best of a crummy situation.