To “waterproof” a house is to make sure that no water gets inside. To “childproof” a house, however, means that the house is a safe environment for children. A popular joke is:
 
“I childproofed my house, but they still get in.”
 
The joke has been printed on many gift items. such as wall hangings, buttons and ecards. “We did have to childproof our home about 3 years ago…but somehow they still get in!” was cited in 2000.
 
 
Google Groups: alt.folklore.ghost-stories
Kids Kids Kids - Enjoy Them!
Lupinia
11/17/00
(...)
>  We did have to childproof our home about 3 years ago ... but
>  somehow they still get in!
   
Google Books
Murphy’s Law
By Arthur Bloch
New York, NY: A Perigee Book
2003
Pg. 145:
Davis’s Dictum
We can childproof our homes, but they still get in.
 
OCLC WorldCat record
You can childproof your home, but they’ll still get in
Author: Dave Meurer
Publisher: Grand Rapids, MI : Fleming H. Revell, 2005.
Edition/Format:   Print book : English : Spire ed
 
Twitter
JohnsFace
‏@JohnsFace
“I childproofed my house, but they still get in.”
3:17 PM - 11 Jul 2008
 
Twitter
Keith Rouda
‏@krouda
How is it no matter how childproof you make your house, they still get in?
7:05 PM - 22 Dec 2008
   
GazetteXtra (Janesville, WI)
Mother of 17 fills her life with her kids
Marcia Nelesen
May 11, 2014
(...)
Despite the sign outside her Janesville home: “I childproofed my house, but they still get in,” Agnes continues to put her family first.
 
Twitter
The Parent Bible
‏@TheParentBible
I child proofed my house but they still managed to get in #home #parentinghumour #parenting http://theparentbible.com/childproof-house/ …
Embedded image permalink
7:57 AM - 12 Aug 2014
 
Twitter
Ricktober
‏@rickolantern
My neighbor told me he childproofed his house. And the very next day his wife came home with a newborn.
Worst. Childproofer. Ever.
8:01 AM - 24 Sep 2015