Yes, wasps are territorial, but this just means that they will defend their nests at all cost. As long as you do not rock their nest (or otherwise cause strong vibration) or stand directly in their flight path, you are safe.
Different nests can be as close as a few meters and their inhabitants will mostly ignore each other. The hornets were about 7 or 8 meters away from the yellow jackets, and I have never seen them fight. If you put some fruit or honey somewhere, they will (mostly) peacefully share it.
European hornets are not aggressive at all, they are just big and loud. When one gets into the house, I usually wait for it to settle down somewhere and then carefully catch it with a glass and a piece of cardboard. We also have mosquito nets on all windows and doors.
Another fun fact: wasps will not spend much time around their nests. They usually leave the nest at high speed (do not stand there!) and then roam an area of multiple square kilometers. When they come back they immediately go back into the nest. Sometimes a single animal may inspect the closer area, but this is rare.
Once you understand wasps, there is not much to fear. I understand your concerns regarding you child/children, and it is probably a good idea to keep wasps at a distance for some time. When children grow up, there is little danger, though. The sting of a single wasp or hornet will not harm a human being unless you are allergic. (European!) hornets use almost the same venom as yellow jackets, only more of it. (In Asia or South America, be more careful!)
Finally, wasps do not want to sting you. Most of the time they are just investigating. When a flying wasp bothers you, slowly and carefully push it away with your hand. Most of the time it will just go away. On the net there are videos of some guy who tries to get stung by various wasps. It is educating to see how much he had to bother them before they did.
