I can remember one which uses innuendo by missing out some of the words - it was on one of the radio satire programmes:-

"Two little boys had two little ****
Each had a wooden****
Gaily they'd play, each summer's day
**** both of course"

Gets funnyish when they get to the line

Someday we'll both be soldiers and our **** will not be toys.

I seem to remember it supposedly being from "The Rolf Harris Dirty Songbook". If you've got the original words it woud be possible to reconstruct it from this.