Even if it's not technically spring, once it warms up enough to be playing outside I start to look around our house and think "Do we really need all of this stuff?"
So one of my favorite things to do is to go through our house and do a huge hunt for donations! Clothes that have been outgrown or aren't being worn, toys that are for different ages than we have right now, decor or appliances that aren't being used - I try to go through everything! Depending on the age of your kids, this is also something that they can help with, since it's never too early to teach them about sharing with others.
If you need ideas for donation spots, here are a few
Donate to charities or thrift shops. These usually use their sale proceeds for great causes, so I first look locally to see if there are thrift stores where I can drop things off since they'll also take household good and books, etc.
Donate to Dress for Success (or similar organizations). If you've traded in your 9-to-5 job for SAHM life, your unused work wardrobe can go to women who can't afford professional outfits for job interviews.
Donate to your local library. We're a house of bookworms, but to keep from being buried in our books, I try to regularly sort out the ones we won't miss, and donate them when our library has its book sales. For all of the good that we get out of our library story times, it's great to give a little back!
Donate to animal shelters. This is one I just learned about: most animal shelters will happily take good blankets and towels for their furry friends!
Donate to neighbors/family/friends. Hand-me-downs are what childhoods are made of :). Help a growing family by just dropping off a bag of clothes that you know are the right size for someone, or make friends with someone on your street by passing on fun dress-up clothes that aren't the right size anymore. It's one of the happiest ways to recycle!