Complaing downstairs neighbour

Hello,

One of my friends who has two kids one is 5 year old and other is 3 year old is receiving complaints from a neighbour downstairs about kids running during the day. He is anyways not allowing his kids to run after 10 PM in the night to avoid any nuisance to the neighbours. The kids are only running sometimes and the noise on the concrete floor is not too high. Is anything the neighbour can do legally? what can be done by the parents to protect their kids' rights in this case?