I'm not saying at all, that its the shops fault.
No one would want their property destroyed. He has been told before about this.
You contradict yourself wanting the parents to pay for any damage, then blaming the shop and wanting the shop to deal with the person.
As I've said previously good luck to you in trying to make the parents pay. There is no disclosed legal basis that the parents are liable for any damage.
If person riding their bike into your gates is going to damage them, then one must question the state of the gates. Properly installed gates would not be destroyed by a child riding into them on his bike. Yet here you are demanding the parents pay for you to have new gates installed.
Then you manage to somehow demand a completely different legal entity do something about it.
We can all get you are not happy about the situation ( and I don't blame you), however the rants and threats of action are simply nonsense and have no legal basis.
Any reasonable person would simply lock the gate so there isn't a way for the child to enter via your property. However, it seems you prefer to demand that other pay you
Disputes like this are not winnable and you will end up making matters worse if you start threatening either the shop or the child's parents with demands for payment
Be sensible to resolve the problem, not threatening