I have lived in a large number of flats and houses during my lifetime, with and without children. As this thread shows, there are many differences in experience. Some terraced and semi detached houses can be just as noisy as some flats and you don't really know how noisy or super critical the neighbours are until you are living there.
Our worst experience was in a lovely solid and beautifully made 5 bedroom, bay windowed house in a Victorian terrace, my favourite of all my homes until we discovered the house next door was let to a bunch of Turkish waiters who came home late and noisy every night after work and partied and gambled all night, every night, and in the day time made obscene gestures to my teenaged daughter every time she left our house. Complaining to their letting agent had no affect whatsoever. However, in that small city we were able to find out the name and phone number of the owner, who we phoned every time we were woken up. She was furious with us, threatened us with the Police, but we persevered and she finally replaced the tenants but it caused us dreadful stress. And that wasn't even a flat!
Some flats are very well made and insulated and as Royandsyl say in the previous message, the Germans are the best but I can only compare with the UK, France and Holland The Germans are the friendliest neighbours. German letting laws are much more weighted towards the tenant than the landlord, which is why flats are so popular there.
Look at the lease carefully, some will state that carpets must be laid in all flats and this does keep the noise down but in my experience can interfere with underfloor heating. Visit the area in different times of the day and evening; chat with an existing tenant if you can. Nothing can replace some serious homework before you sign, except a big dollop of good luck!