My kids and the neighbor's kid are all in the same kindergarten group. Despite having plenty of interaction there, they seek even more contact. That's not bad in itself, of course, but it's annoying that they climb onto the top of the swing set in order to see each other over the hedge and across the street - and then they yell really loud. 

It annoys us parents that:

1. they climb so high just to see each other. (The hedge is dying and we're forced to put up a fence this year; we're contemplating making it *really high.*)
2. they yell so loud that the whole neighborhood can hear them. I suspect several neighbors might be annoyed by that, and personally we don't feel that's an appropriate way to communicate.
3. their yelling is senseless bragging or teasing, or promising to come over despite not having asked the parents first.
4. they continue to disregard our commands to get down from there and stop yelling and they're upset when we lift them down onto the lawn and send them indoors.

How would you handle this? Obviously the fence height isn't going to be a practical solution - we want to deal with this properly and personally. 

***Update:*** 

* The problem is compounded because the kids don't understand that the parents often have other plans; either family would have guests over soon, or would be leaving soon; lunchtime or dinnertime soon; etc.
* Most importantly we feel that the **neighbor kid has a bad influence** on our kids: spoiled single child who only plays with toy weapons, and visits also always includes mobbing of our youngest. If the interaction would be more balanced, we'd be more inclined to let them play together (in either home and either yard, location doesn't matter).
* We have a nice relationship with the adult neighbors, but evidently our opinions differ regarding good toys and acceptable play. We do let our kids visit occasionally, and vice versa, but usually we have to deal with the aftermath of the bad influence and the destructive abuse of their toys as weapons.