how do i get purcHASED songs on my iPhone thru home sharing

yyour sons devices need to be signed into home sharing with your Apple Id. Settings-music-home sharing. If the music is purchased through iTunes and his phone and iPad are running iOS 8 or up you could set up family sharing which would give him access to all of your purchased content without using your Apple ID on his devices This would also give him access to your saved payment method for new purchases but it can be set to prompt you for permission for any purchase he tries to make.