Talk to your neighbor, some folks are just unaware of the consequences of having their net connections unlocked and free for all.
Meanwhile you will also have to get down and serious with your kids and tell them point blank what is acceptable and what is not. Issue some good threats as to what will befall them if limits are crossed. And add the words "And I will find out!" for a good measure. Worked for me! Cos at the end of the day nothing beats a good educational talk with em Rugrats..All the best!