It is difficult because the parents can’t just go running every time the child screams – they need to manage the cries (which are often for attention). It is rough on you but they can’t be expected to give in to the child because of you.
Saying that, I have spoken to our neighbour on more than one occasion to ask him if our childrens’ crying keeps him up or disturbs him. He admits he can hear it sometimes but says it doesn’t bother him. I feel I can’t do much more than that.
As for hammering at that time – weekdays or weekends? I was doing DIY on Sunday morning (drilling right through two exterior walls to put in a co-ax feed to a new TV. I could have started at 7am (our girls were up at 5am 🙁 ) but I did other stuff and waited till about 10.30am which I thought was a fairer time to be drilling.
Perhaps have a polite word about the hammering but just joke about the crying – maybe he will take a hint and try to manage the cries a bit differently.