Call the city every single time you see the dog off leash and out of their own yard. It's dangerous what's happening. And if something happens on your property is your liability not theirs! I have a similar issue a few doors down from me, hasn't happened during daycare hours (thank goodness!) and they are very rarely out of the yard, but as soon as I see them out of the yard I call. They send someone out to talk to them.
I have never said a word to them. It's not my job to tell them to keep their dogs on a lead. It's the city's. Anyways, I have 2 dogs, and I would hate for them to know it's me that keeps complaining and retaliate!