Some people write pure drivel, you can have fun and do plenty of things in a garden without screaming at the top of your lungs. We spent summers in the garden, sometimes that just meant lying in the sun reading, sometimes a BBQ, sometimes music, the odd party. We didn't scream every second we were outside, it wasn't always 5 kids shouting at each other.
There is a HUGE difference between letting kids "be kids" and it being okay to spend 10 hours every day in the garden playing loud music and shouting at each other. There is nothing wrong with doing the latter OCCASIONALLY. Being kids doesn't give you the right to impose yourself on your neighbours all day long. Selfish neighbours literally ruins peoples lives. I live in a block of flats that is a crescent with every single flat having balconies facing into a courtyard. There have been parties... when there are people shut their courtyard facing windows. People sit out on balconies, sometimes talk, never heard anyone yelling or screaming. The couple underneath my flat have kids, their kids are quiet inside, and go out for maybe 30-90 mins a day, they scream a bit but not constantly and no one cares, some noise is fine, the occasional persistent noise(a party now and then) fine. But the kids downstairs, being around 3-5, girls, do the loud pitched screaming but their parents don't just let them do it all day long in summer and I wouldn't let my kids.
What about 35-40 flats, probably 100 or so people, for 8 months, nothing, never a problem with any neighbour.
New neighbour moves in upstairs, only people anyone hears consistently shouting through open windows, he goes on the balcony to scream down his mobile. He has a big subwoofer which he imposes on everyone around him. He smokes particularly strong stinky cigs/cigars which comes straight into my flats windows. They stamp with almost every step and they can't for the life of them close a door quietly, they stamp around in the morning, they stamp around at 1am, they slam every door they use over and over again whenever they are in.
They are a nightmare, they've turned a peaceful block of flats in which no one has had any problem at all into a block of flats in which everyone hates one neighbour.
Anyone, with exactly no exception for kids, is responsible for their noise, some is fine, occasionally being really loud is fine, constantly being too loud is unacceptable for anyone of any age.
When you want to be loud all day long, play music inside, go to the park, go to an arcade. be noisy where you won't upset anyone, being noisy where you are effecting other people in their homes is exceedingly selfish.
The OP hasn't said "they had one party then no noise ever again", he said they are extremely loud all day long. That is completely unacceptable.
they'd love that. If it didn't deter them, it would definitely drown out some of their noise, and help you relax in your own garden. We do this, we don't suffer noisy neighbours though , just love Classic in the garden with my glass of wine, what what 
