Contrary to popular belief, just having kids will not cause brain damage in parents.
Being exposed to kiddie songs all day, however, will.
One of the most annoying things of being a stay-at-home parent is the inevitable fact that a.) kiddie tunes are catchy and easy to remember, and b.) your kids will listen to a lot of them. Even with limited TV intake, most of what will be watched is going to be saturated with cutesy little songs, and in the age of cheap and plentiful electronics, many toys for kids have their own catchy tunes.
You can. not. get. them. out. of. your. head.
I have lost count of the days when I had an endless loop of the Doodlebop song, a Baby Signing Time tune, or the ABC song from Quinn's little Alphabet Train Station playing in my head all day long. It's enough to slowly and surely chip away at parental sanity, more so than any number of poopy diapers or wall murals painted with momentarily unattended samples of diaper rash cream.
Sometimes I have to get out the headphones and listen to some Nine Inch Nails or Rage Against the Machine just to try and dislodge the Underpants March from Quinn's "No More Diapers" DVD, a tune that has the ability to attach itself to your brain like one of those face-huggers from Alien. I'm generally a classical music and instrumental soundtracks kind of guy, but such relaxing fare is powerless against the cloying sweetness and easy-to-remember catchiness of such insidious kiddie fare.
All those parenting books at Barnes & Noble? They don't tell you shit about shit. Oh, sure, they teach you how to change diapers or deal with your toddler's temper tantrum without killing him, yourself, or the both of you, but they are absolutely silent on subjects like "getting sticky kiddie music out of your noggin."
Maybe that's a market niche right there.
If you're thinking about joining the Parenting Club (where nervous tics, thousand-yard-stares, and subscriptions to the Bourbon of the Month at the local liquor store are complimentary welcome package gifts with your membership), then you need to prepare yourself for the toddler years. Buy an iPod, and load it up with the loudest, most furious German rage-and-angst stuff you can find. Rammstein is a good start.
Then, when you find yourself humming the Underpants March all morning, you can put on the headphones, and have a cleansing wave of "DU HASST! DU HASST MICH!" shouted by angry Germans at maximum volume flood your brain, hopefully stomping out that insidious little tune...at least for a while.