After reviewing your brief and the target audience and main goal for these shirts, I decided being kitschy and including landmarks, touristy things, etc. was not the right direction. So, instead I created a clean and modern script for each location, while incorporating your logo as a stamp of sorts.
Moving forward, each location could have its own color and font, with the STA logo being the overarching way to tie it all together.
I also included a hashtag for social media use, as that will help these kids connect and share: both during the trip and after (as they are posting photos, tweets, etc.)
I forgot to mention the best part: each design is only a 3-color imprint per shirt. This will keep the costs relatively low for initial orders, as well as reprints!