Hi. Is there a limit on the sound/music level that kids can be exposed to ? In particular what is the allowed max level of music to be played at child care centers for entertainment and during it's use as a sleep aid?

Most of the information from NSW Health in relation to noise levels is directed to excessive noise levels, with exposure over long periods eg Industrial noise
https://www.health.nsw.gov.au/environment/factsheets/Pages/noise-from-public-events.aspx

The recommendations for child care services is related to supervision of sleeping children which says:
Educators should closely monitor sleeping and resting children and the sleep and rest environments. This involves checking/inspecting sleeping children at regular intervals, and ensuring they are always within sight and hearing distance of sleeping and resting children

eg If music were too loud when children were sleeping, it would be difficult to hear children.
I hope this is helpful, but it is difficult to be more specific.