In grad school I studied and developed methods to make programming accessible to young children. At the time, the general consensus in the field was that before the ages of 11-14, children don't typically have the cognitive ability to write programs, even simple ones. Even though I am a professional programmer now, when I was introduced to BASIC at age 9, I definitely didn't "get it." When I got to 7th grade I did.
Radia Perlman did some groundbreaking work in the 1970's to develop technology in the hope that 6-years-old could learn programming skills. Years later, Ken Kahn developed a game/programming environment called ToonTalk. From my personal experience and research, I don't think you can expect kids younger than 9 to build and program robots, but they can start playing with the physical and conceptual "building blocks."
I see from LEGO's literature that WeDo is aimed at children 7-11 years old. Their approach is very sensible: Keep things very, very simple: One motor, one motion sensor, and one tilt sensor. RoboSoccer can wait until they are older.
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