DH and I live in a small semi with DH and DS2 and 3. DS1 lived here before he moved away for work. Up until last year, we had elderly neighbours, who never mentioned the noise from my DS's. Which I think was considerable, seeing we had 3 DS's who were normal boys playing in their own home. Elderly previous neighbours had children of their own who were grown up.
Last year, we got new neighbours with 3 small children. They are about 7yo, 3yo and less than 1yo. (From what I can see of the sizes.) We do talk but don't know each other IYSWIM.
So, during the day, they play, loudly. I find it fine, when I'm home. DS's say it disturbs them doing studying, sleeping etc. They (DS's) both work when not at school/college during non-holiday times from about 6am.
At bedtime next door kids play up, shout, scream, run up and down stairs, but I say to DS's they are kids. The parents talk loudly but don't yell or scream. Kids go to bed at about 9pm each night.
Overnight the youngest one cries a lot. I hear it and roll over. DH hears it and rolls over. I can tell that its not my DC crying. DS's hear it and complains that it wakes them up.
My point is, small children make noise. Their parents are far more invested than me in a good nights sleep. The parents are probably far more interested in non broken sleep than I am. I have said this to the DS's but they don't get it.
DS's should get over it as when they where they same age they were just as bad as next door.
So, live and let live or ask them to keep the kids down.
(Which I won't do but asking for opinions.)