cloudz,
I really feel for you - I have similar prob myself - trying to get our DD into bed then see next doors running wild till all hours etc...
She wants to play with them but it always always ends in tears, its got to the stage where if i hear they are in the garden, i try and not let my DD hear.
They taunt DD, gang up on her - saw him tring to vicously poke her with a metal pole the other day tell her they wont be her friend if she wont do something, smashed something of hers - physically grabbed her etc....
we have a fence up so they cant come in garden, but its still bloody annoying.
I am very very strict on DD hurting another child, thankfully she never has really but i still watch her.
So it makes me furious that these kids get away with anything, well the parents do tell them off but its not effective.
If i were you i would put fences up, even at front, there must be all kinds of fences you could errect...
eventually your DD will hopefuly loose interest in them, but to be hinest i doubt it!