Pop-up cards are one of my favorite easy crafts to do with kids. They require a little bit of prep, but they're oh-so easy to make and the possibilities are really endless. Here's my quick, easy and foolproof way to make a lot of card bases, really quickly.
1) Start with a stack of colorful construction paper. Cut it in half, hamburger style (that's horizontally, vertically is called hot dog style). And crease each smaller stack down the middle, also hamburger style.
2. Cut a separate stack of paper into quarters and crease each of those new stacks in half, hamburger style. While the stack is folded, use sharp scissors (the sharper the scissors, the bigger your stack can be) to cut two lines into the fold, about half of the way through the paper. Larger cuts mean more height and dimension for the eventual pop-out item, smaller cuts mean less. At the end of step two you should be able to unfold the paper and have it look like this:
3. Literally the only tricky part. Fold your stack back in half along the original crease, but reverse the crease between the two cuts. This is easy enough to do, but may take some practice to get right. Press down hard, emphasizing both the original crease and the new one formed from the paper between the cuts.
4. When you open the fold it should look like this.
5. Carefully pull the first sheet off the stack and using the out of focus glue stick that you can see in the above picture, cover the back. DO NOT put glue on the piece that sticks out.
6. Lining up the folds of your colorful half sheet of construction paper and your quarter page with the pop out, glue the two together. And you have the base of a card!
7. You can make just about any shape to be decorated and glued to the piece that sticks out. Make sure that the piece isn't taller than the card when glued on, or it will stick out of the top when the card is closed.
Once you get comfortable with the basic pop-up base you can experiment with the form. Make multiple pop-out stands, use the same color paper for both the pop-out and the background piece for a more uniform appearance, really, the sky is the limit!