Well, that's really up to you! It's a casual environment, we'll be outside in a ranch area. Weather??? It should be pretty mild 70's, 80's (knocking on wood) Mary's wearing a fancy dress, Aaron will be in a suit, but if those types of clothes aren't your style... don't worry about it! Jeans are fine... That being said, pictures last forever, If you wear the ratty old t-shirt we will notice!
Ask yourself this.... Will they have fun at a wedding? Will YOU have fun at the wedding if they are there? If the answer to both of those is yes, then bring 'em on! If not, it might be time to call in the babysitter.