I read about it here: http://www.ehow.com/info_8360947_sims-cheats-baby-gender-watermelon.html
That's where I first read it too.
I believe that this is not a reliable site though.
You believe correctly. In fact, it shares one common flaw with with Wikipedia in how all of the information is user provided. The difference is (and it's a big difference) that this site doesn't require citations and there's no behind the scenes discussions about the accuracy or validity of the articles.
When the Sims 3 base game first came out, users copied and pasted information there from anywhere they could. Mostly from the Prima guide, but where that didn't provide information, they copied it from anywhere else they could, just to fill the void. I've seen speculation from the official forums (which turned out to be false) posted there as fact, and someone even copied and pasted a list of cheats from the Sims 2 and said they were for the Sims 3. While most of the codes are the same (or at least similar enough to not raise suspicion), the one that stood out was the "boolprop" cheat. As we all know, this code was
not carried over from Sims 2, and was, for all intents and purposes, replaced by "testingcheatsenabled."