The path to the Dark Side is said to be easier than the Jedi way, closer to adult thought patterns and the everyday world. Sith masters don't have the luxury of stealing Force-talented children from their families—the Sith spent centuries one step ahead of the Jedi, and caring for a baby would be a severe impediment on the run.
Although the idea of Darth Sidious with a baby Darth Maul on his back has a certain bizarre charm, it probably didn't happen that way.
Did the Jedi Have It Coming? [1]
The more I read about this stuff (especially stuff like Jar Jar, Hidden Jedi? [2]) the more I have to ask just how deep is George Lucas? Or is there too much being read into his series?
[1] http://www.space.com/sciencefiction/movies/dismantling_jedi_order_000418.html
[2] http://www.space.com/sciencefiction/movies/jar_jar_holy_fool_000414.html