It might be true that attention spans for children are not as great as they used to be, But Sesame Street was the first programme to be shown on British Commercial Television in an hour long format, with no breaks for adverts!
This was a requirement before 'Childrens Television Workshop' would sell the programme over here. Clearly it was a programme with little or no 'pester potential' to put parents off allowing their children access to it.
Putting up with children thinking the alphabet ends with "Zee" rather than "Zed" seems a small price to pay.

Nigel