Can't get include() to work at all - what am I doing wrong?

[alexwebb2]

In parent.lua:

print("In parent.lua")
include("child.lua")
print("Attempted child.lua inclusion")​

In child.lua:

print("In child.lua")
​

What FireTuner shows:

parent.lua: In parent.lua
parent.lua: Attempted child.lua inclusion​

FireTuner shows it jumping straight from the two print statements in parent.lua without ever executing anything in child.lua.

I've include both in the <Files> manifest, and tried various combinations and orderings of <GameplayScripts> references.

What am I doing wrong? What's the correct way to have one custom Lua script include another one?