If you need to speak to or discipline a Junior, then this must always be done with either a Parent or Team Manager present.
If for example you want to catch a Junior at the end of a XC round, then you can speak to them and just say can they report to you at the Secretary’s in half an hour with their Parent or Team Manager. Or an announcement over the PA system if you have one, to this effect.
You should never put yourself in the position of entering into a conversation or disciplinary matter without their adult representative with them. This not only ensures the Junior has support by being accompanied, but also is protecting yourselves when in this position.