This from Money Dec. 2005:

At what age do children start to develop “brand loyalty”?

A. Six Months Old
B. Two Years Old
C. Four Years Old
D. Seven Years Old

Answer: B. By the age of two–really, two–kids can recognize a favorite brand on store shelves and let you know they want it, with words or gestures, says James McNeal, a former marketing professor at Texas A&M. (In fact, his research shows that babies as young as six months are able to recognize some corporate logos and mascots.) Once the brand lightbulb goes [on], children quickly learn the art of the nag: Kids ages four to 12 influence– that’s putting it nicely–an estimated $300 billion of their parent’s purchases annually.