Six o clock in the morning is very early, but you could close the windows and buy a fan .
I think I wouldn’t say anything (to the neighbours anyway) as you have to live with the neighbours all year, not just for a few weeks in the summer. We used to have neighbours living across the road from us who had a young boy who used a heavy, full size football to bounce, and bounce, and bounce.......... It seemed to never stop, all Spring, Summer, Autumn, and any good weather days in Winter. All school holidays, all day and every day. All day long at weekends. Every morning before school, every afternoon after school. Unfortunately the family only went out occasionally, but it was bliss when they went on holiday. We endured it by ignoring, and closing windows. One day I came home from work with a terrible migraine, the bouncing of the ball was horrendous, making the migraine much worse. The child was regularly asked to stop by Mr M, but didn’t. We had to endure it I’m afraid, including enduring the migraine. Eventually the family moved, and the boy from up the road who used to play with the bouncing ball boy, grew up and moved out. So now peace reigns in our little Close again.
However, a little footnote, just one time Mr M tried to have a little word with the parent, about said ball bouncing, he was rewarded with a torrent of verbal abuse, plus almost unbelievably, the comment that had Mr M said something to the parent on my migraine day, the child would have been told to stop! On that day at least!