shorts/sweats/t-shirt outfits.........so they can wear the shorts under the sweats in the mornings/evenings and just take off the sweats if needed mid-day
zip-off pants.........they make 'em in small sizes too.............just zip the legs off when it's warm, and zip 'em back on when it's cold
and one sweatshirt and one fleece for each..........and their hats/gloves because when we went in February it got pretty cold.......we did okay with t-shirts/sweatshirts/sweat pants except we did end up buying gloves and hats.........the breeze on the rides can get pretty stiff!
this way, they have pant options, they'll wear t-shirts, and then if it's a bit cold sweatshirt or fleece......if it's really cold, then sweatshirt AND fleece
AND if you get lucky and it's really warm, they still have their t-shirts and shorts!
When it was cold last year, too, on the look-out for sweatshirts, we bought those cover-up towels that look like Pooh and Mickey to try to keep the kids warm...........it worked like a hooded blanket adn was so, so cute.............I am taking those this year for getting out of the pool........the water's heated, but the air isn't!