It is too late for this summer.
Not so long ago, my kids went to a week long camp with their classmates. I could not gave them a ride. On the night before they left, out of blue I got the idea of writing them a note on a piece of scrap paper and tugged it somewhere they could find easily without effort. It was a total suprise to the kids and their mom. I did not remember if they contacted us or not during the week, they sure aknownedged the little note after they returned home.