If children continue to pass, but do not stop the participation of others I usually have a chat with them 1-2-1. In all cases so far they have started to take part more after that.
For those whose behaviour is interrupting our circle I have found it useful to use this behaviour as a topic for our community circle – group problem solving. We have rule of "no naming, blaming, or shaming" when talking about personal issues like this, so we discuss how the behaviour makes us feel, the effect it has on our community and what we can do about it. Quite often the children take it upon themselves to remind these individuals of the caring agreements which is great handover!! Sometimes they decide that those people should leave our circle. The children taking ownership is really powerful and I consider myself very lucky that we don't often get to this point.