This is, of course, a matter of personal opinion. It also depends greatly on how you define “juveniles” and how you define “meaningful participation.” My own view is that it is not important for juveniles to participate in the “affairs of society.”
I would define a juvenile as anyone under 18. The younger the person, the less business they have (on average) being involved in the affairs of society. I would define “meaningful participation” as being able to vote or to participate in things like political rallies.
The main reason why I say this is that many juveniles simply do not have the background to participate in a meaningful way in most of the affairs of society. Your typical 14 year-old (and even many 17 year-olds) does not pay any taxes and does not have much knowledge of the system of taxation. The typical juvenile does not understand many of the issues that are important to our society. For that reason, it is not important that their voices be heard.
I have nothing against having some juveniles participate in public affairs. A young person who really cares a lot about an issue should have the right to do things like attending rallies or trying to get a legislature to take a certain action. However, this is not the same thing as saying that it is important for all juveniles to be involved in the affairs of society. Most juveniles simply do not know enough (or care enough) for it to be important to make sure that they participate in our affairs.