Its not a myth, its on Wikipedia!!!
Just to clarify; TC's Wikipedia quote says the early research was wrong and that babies are born with a fully functional blood brain barrier...

Wikipedia is pretty cool charlotte, my uni course is full of pretty technical medical stuff, I use Wiki a lot (at lot a lot!) and I get really good marks when I put my mind to it. I've never come across a dodgy entry and I prefer to use it over the thousands of dollars of medical textbooks in the house. Though I wouldn't admit any of this to my lecturers...
I used to be very cautious about using it but I've owned textbooks that are not as concise or accurate.