You say you don't know many children at all, Alegrias - so presumably you don't know how children between 11 and 17 react to traditionally presented lectures. Their attention wanders, that is how they react, and once it has gone, it is very hard work to get it back. An auditorium full of bored youngsters sitting in tightly packed rows within kicking distance of the seats in front of them is a powderkeg.
The adults in the audience are probably more sophisticated in their reactions, but they probably include plenty of people whose scientific knowledge is at or below that of the 11-year-olds. Explanations have to be at a level that children and science virgins can follow, and must contain a lot of graphics and/or simple and obvious experiments that illustrate the theme and - an important detail - stick in the mind
A school lesson is constructed in a completely different way from a lecture to students or people who already have a scientific background and are seeking more detailed information. Some celebrity scientists with highly public profiles can put over complex ideas so that they can be understood by a five-year-old. Others are not understood by their PhD post-grad students. If someone has already been shown to be able to put things over on the media, and are known to their audience, they are more likely to be in the former group - they are educators, not just experts.