I never did the penpal thing, but when she was younger (2-3, she is 5 now) her father was in Okinawa Japan, and she missed him terribly. My parents would spend a lot of time with us, take us to fairs, and fun stuff, where she would always get free balloons.
To make her feel better, we would write a message on it, give it kisses and send it off in the air to her daddy in japan.
I would always tell him ahead of time when he called so he could tell her the next day he got the balloon.
Now that my parents have moved away, we send the balloons to them.
I would suggest that you get a pen pal through an organization like the Boys and Girls Club or something similar. I’m in Southern California and all the environmentalist wackos around here would have a seizure if I intentionally released a balloon into the air. Sigh….
you might want tot use a PO box instead of giving out an actual address, or maybe use an email address as a contact.