Hate to tell you, but according to Carnegie Mellon researcher Erik Thiessen, the exhausting sing-songy voice you use with kids--after consulting their Lame-Name-o-Tron, scientists called it Parentese-- helps them learn language more quickly.
Specifically, it helps them identify word boundaries within an otherwise constant stream of syllables. The result: they pick up words up to 25% faster than kids who are spoken to in more monotonic adultese.
Thiessen also told WebMD, "There may be something about the simplified way that people talk to infants that makes it easier to break into a new language and figure out what is going on," a finding based, presumably, on his earlier grad school study of Alec Baldwin's French teacher on Saturday Night Live.
'Baby Talk' Speeds Language Learning [npr.org, thanks to DT reader my wife. it's family week here at daddytypes.]
Abstract: Infant-Directed Speech Facilitates Word Segmentation [infancyarchives.com]
Baby Talk May Help Infants Learn Faster [webmd.com]
Speaking Parentese: "It's spoken around the world, because we all love to do it"! [umm, not really, pbs.org]
French Class [snltranscripts.jt.org, the transcript doesn't do it justice]