Claire, I hope you can get this taken care of...I can't believe they will not make an exception for that situation.

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I've grown certain that the root of all fear is that we've been forced to deny who we are. ~ Frances Moore Lappe

I show up early with my kids for events all the time. I bring stuff for them to do. Or have one of the older kids, or my or hubby walk around with them for a bit until the show starts. We just leave that persons coat in there seat. If the coat is there at least you can show that the person is in the building, just not seated at the moment.
Yes I will save a seat or two for Grandparents, but that is it, not a whole row.

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I have nothing to declare except my genius."
- Oscar Wilde (1854-1900) upon arriving at U.S. customs 1882

I always feel uncomfortable trying to hold seats. Especially if it's a crowded event, I just feel bad telling people they can't sit there! I don't see a problem with holding a few seats, but it is very irritating when people try to reserve the entire row.