AIBU to think this is unbelievably selfish

It's worth a try. We are so tired any bonhomie we might have is going fast. We don't want to fall out but we are fed up with their lack of consideration. It's not like we have big gardens. We are all on top of each other whcih i think means we should be more mindful of one another not less. The neighbours on their other side are friends of ours and in the same predicament

Would the squeaky springs benefit from a squirt of WD40? You could suggest that to the parents, perhaps making it sound less like a complaint by also saying what a lot of fun the children get from the trampoline (which is true, even though it is not fun for you at 6 am)

I do understand the early summer mornings but always stopped my own children playing noisy games in the garden until a more reasonable hour because it wasn't fair on the neighbours. I know what it's like to have children up with the lark and desperate to play but I also think they are never too young to learn about consideration for others. If it was 8am I wouldn't mind but 6am is just not fair, especially at weekends

This is just the sort of thing that could get neighbourly relations off on a bad foot and there is no easy solution I'm afraid. Personally I would be inclined to invite the neighbours round, ply them with tea/coffee and cake, then offer them a gift of WD40 as you've noticed that 'when the children play on the trampoline in the early morning the noise wakes you up'. You've then identified the problem, shown a willingness to help with a solution - and hopefully given them a face-saving way of responding. They could of course take huge offence and storm off, but then you'll know what sort of people you're dealing with. Hopefully they will apologise for their thoughtlessness and scamper away to tell the children there will be no trampolining before 9am in future.

6am????? oh my word. I am a childminder and never allow children into garden before 9am, try to leave it later if I can . Also explained to older kiddies not to be shouting and screaming as our neighbour works nights (although their dog barks constantly!!!)

Not sure what you can do tbh. Maybe try to have a chat and jokingly mention you don't need an alarm now they have moved in

Difficult one? my own DGD aged 6 and 4 are also up with the lark especially in the heat? my DD and SIL are inclined to keep them inside until at least 7.30 due to worrying about sleeping neighbours! But I guess people don’t think about this.
I probably wouldn’t say anything as the warm weather won’t be for ever? I would may be invite them round for a cup of tea etc and then when relations are more established ask if they wouldn’t mind keeping the kids in until a more sociable hour.