Green’s Dictionary of Slang

packet from Paris n.

also parcel from Paris
[? clichéd identification of France with sex, though not usu. with procreative intercourse]

(Aus./N.Z.) a baby.

[Aus]S .J. Baker Aus. Vulgarisms [t/s] 11: packet from Paris: A child, especially an illegitimate. Obviously related to F.L. [crossed out in pencil].
[UK]Partridge DSUE (8th edn) 846/2: C.20.
[NZ]McGill Dict. of Kiwi Sl. 81/1: packet from Paris a baby.
[NZ]McGill Reed Dict. of N.Z. Sl. [as cit. 1988].