I think the risk of a "junior forum" is that it will be identified by people looking for "children" to target - at the moment, the junior members are protected by the fact that they are indistinguishable from the adult members...but a junior board will instantly identify which members are younger
We do share a lot of personal information amongst us here which can be seen by anyone (e-mail addresses, photo's, holiday plans etc); it would worry me if junior members were somehow singled out, as they can be such vulnerable targets