The president wants to kick off his "national service" aspect of his agenda. This speech is 100% part of his political agenda and is structured as such.
"Oh, me, he's just talking to the kids about happy topics we all agree on"... no... he isn't... he's going to talk on things he is going to need legislation to accomplish and to do so he's going to bypass the parents.... "daddy, why don't we do more to help each other?"
The president's already laid out his agenda... why aren't you aware about the things he's set out to do?
Its not like the president is going out there and tell them to exercise more and brush their teeth.
edit: why does the president need to speak to the children and not the adults? What's gained from this? If nothing is gained then why do it?