I say if you really want to wear the kilt (of course you do), wear it and go all out. skimp on other clothes. I would assume with the amount of kids that normal day to day would be casual. I'm sure you can get away with one less shirt and shorts, since you might be on the deck with no shirt and bathing suit shorts half the time, and can re-use the shirt you only wear for 1/2 the day. And if not most do offer laundry service.