Yeah I love it how everyone rushes in to laugh or try and support the parents, f@#$cks sake.
Here's what's really going on.The shrieking chimp noise that kids make as they free play in the back yard is a constant irritation to many many people. It's not cute, it's not some "fun thing" it's a really nasty rock and a hard place for many neighbors. Your kids are not doing soft little giggles - no doubt they are bored out of their tiny minds and screaming around the back yard is their only form of recreation. Oh so much joy to be had right there.
You're very lucky your neighbors don't start blasting heavy metal music in your direction, or a chain saw or other equally offensive noise because your kids are not the "Joy" you think they are.
Ok - well here's the thing. This is what you could do. First up admit and accept your kids are going to make an ungodly amount of noise. Stop being in denial about that, they do make noise. People do not like it.
Secondly start to consider how to reduce that noise, and when noise is acceptable and when it is not. Clearly no one wants to hear screaming out of control children past 6pm- use your brain. Kids should be settled down, not screaming around the block disrupting everyone else's evening routine and being a noisy pain in the arse that you know they are.
By about 8pm they should be in bed if they are too young to reason with, and that age that make that hellish noise. Weekends- we can cut slack but when that magical 8pm at night rolls around they should be in lock down, then bed. Also hell no to starting to early either - no screaming at 8am in the morning. Breakfast, routine, organized = not screaming.
School camps, trips to away, doing interesting indoor things, keeping the kids engaged and busy so they don't do peanut crap like scream and think that's fun all day every day. Parenting, time out, and giving them a bicycle and helmet to roam away elsewhere is also a legitimate thing to do to help burn off this excess energy. Swimming lessons, supervised walks - also calm down a house full of fractious kids too.
So yeah sort that out.
I'm a neighbor too.