1) Make and decorate paper airplanes. If you don't know how, don't feel bad. I found a great website to help you step by step. My boys love to fly their airplanes from the upstairs down to the main floor.
2) Make your own play-dough. It's easy and you can have your kids help create it and then play with it.
3) Make something grow together. This is a perfect time to get seed packets at stores since they are bringing out all the spring items right about now. I love to see the excitement on my kids faces when they see the seeds grow into something new. Ideas can include, marigolds (which if you put in a clear plastic cup towards the edges you can see the roots grow), zinnias, sunflowers, etc.
4) Get outside in the snow and build a snowman or snow fort/igloo. And if you live somewhere that doesn't have snow (I envy you right about now!) then make an indoor fort with lots of pillows and blankets.
5) Have an indoor scavenger hunt. These are always loads of fun.
I hope I have inspired you to get up and have some fun even when the weather begs to differ. Kids are only little once so make the most of the time you have with them and have some fun!