Some actual quotes from the video:
Talk to a child as if you were talking to another adult. Don't use
baby language. Don't even use oversimplified language. Talk to a child
just as you would talk to another person. You will find that by the
time they're three years old, they will have an amazing mastery of the
English language, and will be able to tell you all sorts of things
about what it is to be a child that child psychologists have been
longing to know, but could never get out of children because all
children have been taught to be Mickey Mouse.
Based on the context, he is saying that you should use adult vocabulary and grammar to build up a young child's communication skills. Using "baby talk" (in his phrasing, talking like Mickey Mouse) doesn't convey information or help them develop into a productive member of society.
Treat your child as an adult. Treat the child fairly. Don't talk down
to your child, talk up to your child, and you'll find that they can be
A child brought up to be a "child" is a bore and a pest. It's a
cutie-pie, itsy-bitsy sort of approach that to my mind is nowhere.
It's what Disneyland is made for.