There are two lads that walk their dog past my house every day, about 13yrs-ish in age. A couple of years ago their dog was growling/snapping at my toddler and my Ddog got defensive about it, and now absolutely hates their dog.
They’ve recently taken a big liking to Dcat, she’s friendly and will walk up the drive to be petted but if they stand and pet her, their dog winds mine up through the gate (growling and barking etc) and my Ddog starts to bark and is very agitated.
They don’t walk away when this happens, they stay there and stroke Dcat for about 10minutes, they even sit at the end of my drive and fuss her. At first I was bringing Ddog in when it happened but then, they started trying to take Dcat home. At first they would “chch” her as they left so she would follow them. And last couple of times they’ve picked her up to walk off with her
I stopped bringing Ddog in hoping it would scare them off a bit but now I’ve caught them telling my Ddog off through the fence and “squaring up” to her 
The whole time this is happening their dog is pulling them off their feet, growling and barking at mine but they still just stand there. My DH once politely asked them to move along as Ddog was wound up but it hasn’t stopped them.
They seem very obsessive with Dcat and if she’s nowhere to be seen they will “chchch” for ages and even call her out of my house. I genuinely don’t mind people petting her but it’s clear they want to take her 
With them being children I haven’t a clue what to do or say. Any help please in what’s appropriate to tell them?