My 9 month old Labrador is a lovely dog- he's really getting to grips with day to day routines, and doesn't have a bad bone in his body. He is awful for jumping up at new people arriving though, and big enough that it's really becoming a problem. He gets hugely excited when someone new arrives into the situation, and will relentlessly try to jump up at them, requiring lots of restraining for the first 15 or so minutes. He can really knock a child, especially ds (6). It's especially stressful on walks, where he cannot be off the lead at all, unless NO ONE else is around.
How can I discourage this?