Want a fun treat to arrive at your home? Want your kid thinking a bit about math? Public Math will send a postcard (with a math image and question on it) to you for nothing. You can even have them send one to another friend as well. They’re spreading the love of math.
There’s plenty of other fun stuff on their site too.
You can print out some coasters to make fun designs.
You can print out some zines (I highly recommend the talking-math-with-your-kids ones).
They’ve even got an app for finding math out in the world.