A Bronze Coin story is an all-ages story. You could read it to Bobby at bedtime.
A Silver Coin story may contain adult situations, emotional/sensitive storylines, mild adult language, mild sexual situations or non-explicit descriptions, and/or some violence or non-graphic descriptions. A typical Cosmo McNaught or Lucy Radcliffe book would be a good example.
A Gold Coin story may contain emotional/sensitive storylines, explicit sex, violence, or adult language. These would be the steamy Harlequins Maddie Wheeler tucks under the mattress or the grisly murder mysteries Harrison reads in his downtime.