Attending summer camp is but one way to encourage learning in the summer. There are also lots of other things kids and families can do to keep their minds and bodies active all summer long. See suggestions in the links below.
Your local public library (or the public library in the city you are visiting) will have lots of activities and programs to keep kids reading and learning all summer long. Libraries often publish reading lists, organize reading clubs, invite speakers, and have cool makerspaces where kids can tinker and play. Resources are often free for out-of-town guests.