There was a time in a previous home when 2 or 3 children were regularly visiting their DGP and being a nuisance, aged about 4 yrs, running through my garden for their ball etc and trampling plants, shrubs, daffs. I didn't want to make a big deal as they had older siblings/cousins who might decide also (or not) to be a bigger nuisance.
So I went out and brushed the drive while they were playing around. I smiled and waved at them..... they knew me to see as their granny lived so near. When the ball came up to me I threw it back the first time. Second time I let them come to me for it.
Asked them did they like flowers, would they like to have a flower for their granny. But only adults were allowed to pick a flower. So a flower was chosen for granny.
Then I showed them the mummy plants and the baby plants, explaining that if the baby plants got trampled the mummy plant would be sad. And if the mummy plant got trampled the baby plant would have no family.
I asked them if in future it would be best if the ball didn't go near the plants but if they had to would they please be very very careful when needing to collect their ball and tread slowly and very carefully. Also that I'd love it if they gave me a wave when they did this. It worked and I'd no more bother.
However, Marieeliz is in a different position and must feel quite vulnerable, the children seem old enough to be some distance from their home. Some parents get all defensive when approached about their children when they should think it through.
A neighbourhood watch commitee would be a wonderful approach, i.e. representing the area regarding unacceptable behaviour.
Perhaps when janc mentions the police it's not so much being a heavy hand so much, more like the community policeman on his bike 'coming across them in action' and then being able to speak to the families the unpleasant behaviour of their children'. Or community policeman speaking to families regarding a few reported concerns of children behaving in an unpleasant manner.
Sorry for long post.