You can't solve this legally, as the law seems to be on the child's side but there is always payback.
Here's my story:
2.5 years ago, the single lesbian above got a brand new baby ( she's lesbian and I've never seen her with a man but somehow she got a baby, her first. Thank god for the miracle of advanced medicine!). For 1.5 years, the baby cried almost every night. I didn't even think of complaining because I realised that crying is out of anyone's control and it's unreasonable to demand that the child is calmed instantly. I got really tired, it interfered with my personal and professional life, it was as if I had a baby of my own but I accepted the situation. However, after 1.5 years the baby stopped crying and started "talking" and running and here is where the fun part starts.
Both the mother's stride and the baby's jogging are so severe that they shake my hanging ceil light and they wake me up ( I was getting that at any time between 7am and 11pm). The mother stride has always been like that but it didn't bother me as it was not happening very often. I got in contact with her and told her to try minimise this type of noise. Since we are in Germany and we don't really talk to or have contact details of neighbours, I wrote her a polite, almost defensive note and put it in her postbox. Her answer: "If you can't have a normal face to face discussion, I'm not willing to change anything" ( interestingly, the only two face-to-face interactions we had had, were initiated by me, she hadn't even said "hi" before that. Anyway, different discussion for another time). Two months later, I meet her in front of the building and start a discussion on the topic. Conclusion: "How do I even dare to suggest to move the baby to another room" ( apparently I had suggested that in my note ). No intention to address the problem, no intention to collaborate.
That's when I realised I needed to solve the problem differently: I bought a powerful sound bar ( I've always wanted one of those anyway ), placed it on the wardrobe in my bedroom, facing upwards, and created a script which plays randomly 3 types of 30-sec sound samples: baby cry, porn and scary movie. The sounds are played every 30 to 50 minutes ( this is important* because, if police shows up, it minimises the chance that they hear the sound coming from your apartment ) and it doesn't play between 2pm and 4pm as this is the official rest time in my building.
I was starting the script every morning before going to work and stopping it every evening when back. Over the next 2 months, she showed up to my door at least 5 times, complaining about the weird noises: she started with a cool attitude and jokes around how much porn I watch and ended yelling, telling me she had called police and they had been in front of my door and threatening she will sue me.
Interestingly enough, she was the only one complaining even though I share walls with 2 other neighbours ( I guess it's because single mothers and their babies are always at home, while other people leave during the day). Fast-forward: I haven't seen her around and I haven't heard any noise in the apartment above since November last year. Her name is still on the door and on the postbox, so she still lives here, theoretically.
Moral of the story: dear parents try to be collaborative when it comes to the noises your babies make
(*) A more advanced script can be created involving a camera or a mic to detect presence in front of your door ( so that you trick police )