Quiet musical toys with duct tape
I can't stand the volume of some of my kids' toys (I'm looking at you, riding toys!). For toys that don't have a volume control or for when low volume is too loud, I place a piece of duct tape over the speaker. The sound still comes through, but isn't as loud and shrill.
Candidates for this hack: anything with Dora the Explorer's voice, Spongebob's voice, Barney's voice, Bob the Builder's voice, horribly jingly music...
And you don't have to use the boring, silver stuff! Check out this cool zebra tape!