I have taken my lot to festivals and its been fun. My favourite photo is of DD2 at 6 months old, butt naked and surrounded by empty beer cans and hairy arsed bikers :o The kids had a whale of a time but it wasnt exactly relaxing, you need eyes everywhere.
The problem with this is that its neither one nor the other. With a festival you know what to expect so you go prepared, there is always something going on to entertain you and any kids, there is always food available (if you are prepared to risk it!), usually a fun fair etc too. This is just going to be a load of strangers in a field, no entertainment, no food outlets, no fun fair...Giant Jenga isnt going to cut it! Then you chuck in the added stress of getting ready for and attending a wedding, its just isnt going to work.
I suspect the bride is imagining everyone round the campfire, chatting, singing etc the nights away when in reality you will have the stressed parents who are trying to keep to their routine in an impossible situation and roaring at anyone who farts within a 5 mile radius in case it wakes up their little darling. Uncle Knobhead who gets pissed within 5 minutes of arriving and decides to introduce himself to everyone by walking into their tent uninvited and not leaving. Auntie Knobhead who appoints herself as camp commandant and tuts and complains at any child who dares to look like it might be having a nice time. Cousin Knobhead who decides that communal camping means that someone else will look after her vile brats while she gets afloat to the tonsils on Blue WKD. The friend of the groom who cant accept that he isnt 21 anymore, smokes weed around the kids and tries to get off with any female adult in the vicinity, marital status unimportant, then calls you a lesbian if you turn him down. The bitch friends of the bride who look down their noses at anything and anyone, especially someone who has dared to bring a child with them, refuse to speak to anyone outside their select friendship group, and at least one will at some point be discovered by a shocked MotB getting shagged from behind in public by the grooms friend mentioned above,......
Should I go on?! :o