Sorry, another neighbour one but I need an outside opinion. Totally prepared to be told it's me with the issues, it seems things with neighbours have being going on for so long that things that shouldn't annoy me now are... it's getting to the stage where me and DH are genuinely thinking about looking for another house.
We rent and live in a 3 bed semi-detached house, the house joining us own their property. We have two young children (2 and 10 months) and they have 6 aged between 1 and 16, we've lived here almost a year and it's only in the last few months that things with the neighbours have become strained. I can't think of an incident that set it off but it all started about Christmas time.
We live at the bottom of a cul-de-sac, we both have 2 parking spaces, one directly outside of the property and a parking bay across the road. We have 1 vehicle and they have 2 (I've tried to provide an illustration!) just before Christmas it became increasingly common that i would arrive back from work around 5.15pm and NDN would have both of their cars parked in the spaces outside of the properties, theirs and ours. I would park across the road and then have to carry DS1 and DS2 into the house. I asked NDN politely if they could leave our space free as we needed it, especially when I was taking two children into the house and it was raining. They apologised but nothing changed, they still park in our space 4-5 days a week. When their parents visit they park across the two parked cars (ours and theirs) blocking us in.
For what it's worth I don't know what they do for work/if they work but they are both in the house almost all day. I have just returned to work after maternity leave so have been home myself to notice their comings and goings.
They do a lot of DIY on their house, this is fine, they are entitled to do it and if it's very noisy I take the children over to my parents or out for the day. I don't expect absolute silence from them. However, last weekend they decided to fit a new fireplace at 11.30pm on a Sunday evening. Obviously this woke up DS1 who was terrified of the drilling (as was I to be honest) and wouldn't settle until around 2am. DH went round to ask if it was necessary to do DIY using tools at that time and that they have woken up our kids, their response was they also had kids and they were awake so it was ok 
this was an extreme case but they regularly hammer, drill, move furniture etc...after 8-9pm.
Now the evenings are lighter the children are playing in the gardens more, ours and theirs, which is lovely. The children are nice enough but if they're outside at the same time as DS1 (2) they do make fun of him (mock his speech, tell him he's a baby because he wears a nappy, ask him to say wee wee and poo poo etc...) so we try to keep DS away when we can. Their parents have heard them doing this and said nothing.
Bedtime for our children is about 7.30pm - this past week the children next door (5 year old twins and 7 year old) have still been playing on the trampoline in the garden at gone 10.30pm. (They are back at school
and it doesn't seem to matter if it's a weekend, school night, holidays etc...) They don't play quietly and even had a water balloon fight last night, in the dark. Its not my business what anyone else decides to do with their children but as my DSs window backs onto the gardens he has been disturbed every night and woken up crying, so it's started to affect mine.
Today I spoke to the mum and just asked if it was possible to remind the children to not scream and shout later in the evening as my son was being woken. Her response was "it's doesn't mattter what you think, it's not even your house!" And she walked off 
so it seems that because they own their house and we rent we just have to put up and shut up.
I don't like confrontation, I don't want to cause friction with the neighbours when we have to live here. I'm thinking of contacting our letting agent and landlord but don't know if I'll get anywhere. Has anyone who has rented had anything similar with owners? Is it worth speaking to them again, writing a letter or do you think I'm wasting my breath? I've read a lot about owners having problems with renters and what to do but not the other way round 