They don't have to give you the blues. They're not only a great day to enjoy some tea and conversation, they're actually a surprisingly good day for photography!
Take your child outside in their raincoats and boots--let them play in some puddles--there's nothing like the pure joy on a child's face when they're getting dirty! Teenagers love to get wet too--don't bother with rain clothes there--just let them roll up their jeans and have a blast!
The light is usually a nice haze or cloudy afternoon when it's raining and skin will look great, plus you can look in any direction without squinting!
Don't forget to protect your camera and lens though if it's coming down, if you're only going to be out for a bit, a simple plastic/ziplock bag with a hole for your lens and a lens hood should do the trick.