My daughters are now 10 and 3. I had the same thought on our trip last year. Here's what worked for us: I had our older dd choose a cute t-shirt from Gymboree from the Big Girls group. Then, I bought our younger dd a t-shirt in the same line in the Baby Girls group. The t-shirts weren't identical, but were close. I did the same thing with their skorts, so the overall effect was coordinating, but not completely identical. I think the line was tropical, ie, palm trees, monkeys, etc.
Once we got down there, we bought Thing One and Thing Two shirts at Universal, just like a previous poster did. Older dd thought that was fun.
Once we got down there, we bought Thing One and Thing Two shirts at Universal, just like a previous poster did. Older dd thought that was fun.