I must say that I read your post and thought " I bet my neighbours think that about my kids". My 3 are 4-11 and in the holidays are out all day in the back garden, especially in this weather. My 11 yr old has just started to play 'out the front' with her friends, but my 2 boys are too young and stay in the back garden sometimes with thir friends round. They can be really noisy and because my neighbours have no kids I'm forever telling them to keep the noise down- but kids will be kids. When I was a kid we would go out in the morning, come back at lunch and then go back out till tea. Then if the weather was lovely we'd be out till the street lamps came on. But in this day and age kids can't do that anymore and so spend more time in the back garden. Like I said, my 11 yr old has just started playing out the front, but she has to keep coming back to let me seee she's ok, and she's back in by 5.
Is your problem more that they may be unregistered childminders or just the noise the kids make. You may just have to grin and bear it till September.