Neighbors are complaining

Dear All,

Recently we have face an odd situation:
We live in a normal multi apartment building. We have two kids of
12 and 2.8 y.o. We have always had a great relationships with our neighbors.
Few month ago I received a letter from the Makelaars who own the building.
The letter was stating that we make a lot of noise and disturb our neighbors.
We went with this letter to our best neighbor who keeps our keys "just in case"
and asked her to translate it to us completely.
And than she said: "Yes, I informed the makelaars that you are disturbing".
My wife was in a real shock due to several reasons.
She could not understand:
1. If we make noise why nobody has talked to us.
2. How could she pretending to be our friend do things behind our backs.

Whatever, I wrote a letter to Makelaars informing them that we are normal family with kids, we don't play
musical instruments, we do not drill, we do not hummer our floor and e.t.c. I required them to replay to me
but they did not.

Frankly, we do not make noise, of course my son plays at home, he might even run from wall to wall, when he
is happy he used to laugh and jump. He is a kid. And it does not happen constantly.
I mean Should I really stop him when he laughs, plays or jumps, it is just normal growing up process.
I really hate that. Anyone knows if they are regulations in the NL? I mean kids are making noise, of course. What can I do about it?
And there is no restriction on the building like: “No kids allowed”.

Any advices?
Thanks in advance.