MrsCs, you seem a very considerate, responsible neighbour with respect for the people living around you. It's a shame more people don't have this attitude to parenting.
Hedgehog, I hardly think an information leaflet is comparable to a poison-pen letter 
When I issued the leaflets I attached a card with a polite message explaining I was unable to sleep, that I have to get up at 5:30am and requesting they try to reduce noise after 11pm. I included a brief summary of local SureStart services and wished them well. I added my name, flat number and mobile number, asking them to contact me if they wanted help or to discuss the issue further. So it was not anonymous, although in hindsight I do see how the leaflets could have come across as patronising or annoying.
RigglinJigglin... I'm not familiar with the rules of bingo; perhaps you could explain them?
PrettyWhiteGuitar, reading the posts is certainly an eye-opening experience. I do feel more empathy towards my neighbours having been made aware of different people's experiences with toddlers.
Yet what the posts also highlight is just how many people lack respect and consideration for neighbours, or feel their child is so out of control they cannot possibly reduce noise at night. It also highlights how many people try to shelve responsibility for their child disturbing others! Your child is your responsibility, and while neighbours are powerless to reduce your child's noise, parents always have option of trying different approaches until they find something that works.
It is also inspiring that many people here DO take responsibility for raising their toddler in a way that minimises disturbance to neighbours. Simple measures like taking child into a different room, using stairgates, teaching which behaviours are appropriate etc are clearly effective for some, suggesting it is not 'inevitable' that toddlers run around screeching and banging walls until 3am every night.
Oddfodd... I believe the parents sleep from around 3am-9am, as this is the only time the toddler is ever quiet for an extended period of time, though he is sometimes active from 6am. Or maybe they are accustomed to his noise and are able to sleep through it. Their kitchen and living room adjoin my wall, and it seems he is most active in these rooms at night.