Put a row of planted-up containers along the boundary. You could just about plant them now with something that will bloom in spring, or be evergreen foliage. Or put supports into them to hold up some non-existent plants "when they come up". You can complain to the neighbours later that those plants you put in were sheer rubbish and have not done at all well. How about artificial plants?
Put a couple of garden chairs outside your French windows to at least look as though you sit out there (possibly cementing them down in case they walk away) You would freeze at the moment, but if you wait until the summer they will have got well into the habit of using the space as a highway.
Park your car beside the containers, so that the neighbours have to walk round it to cross the rest of your drive.
Make a big thing of needing lots of space to get in and out of your car, use a couple of sticks ostentatiously to show that you (or DH, or a visitor who is game to act the part for you) would struggle if there were another car parked beside it.
On bin days, use your drive as a halfway house for the bins on their way from the back to the pavement. Put them there when it is too early to put them out properly, but convenient for you to have them ready for the short distance when it is time.
Be very sweet and nice to them. Tell them you do hope that the little boy won't come to any harm if he wanders into your garden, where there are some rather dangerous plants, with leaves and berries that could cause him a nasty tummy upset - nothing really poisonous, of course, but unpleasant for him.
You could, of course, just ask them nicely if they would mind leaving your drive for you to use, and you will keep off their property in return. It may never have occurred to them that you would prefer that, if they have been used to flats with a little bit of communal garden/yard at the back and a strip of weed-infested gravel at the front.
Shall we reboot our cartoons thread again? 😁