Hi C.,
We took our 3 year old son to see Crowded House with us last week. Here's what I noticed--
Yes, the music was loud, but there were places to walk to that were a little quieter than others, back away from the stage. The space was kid-friendly, except the bathrooms, which were porta-potties, so there's no changing tables. Hats might be a consideration, depending on how cool it gets in the evening, because there's no shelter from the elements.
For what it's worth, Edgefield shows only go until 9:45-10 at the latest, due to noise ordinance/neighbor consideration. We left the show at about 9:15 or so, and while we missed the last few songs, we got out before the parking lot/traffic jam erupted and had an easy trip back into Portland.
Last--while I'm really glad I brought my son (who loves their music), I've seen this band a lot of times and so the distractions of parenting/early departure weren't a bit deal to me. But if this is a once-in-a-lifetime/truly special event for you, do consider the sitter, just for your own enjoyment.
Whatever you do choose--have fun!