You mirrored my kid communication tech experience, except mine was with my neighbor next door. My brother and I were 13 and 12 respectively. The neighbors were two girls: 14 and 12. Bedroom windows about 22 feet apart.
Our list of experiments included:
Written signs
Tin cans
Morse code circuit
Wired handset
Walkie-talkies
The fun lasted a couple years until puberty struck.