Creating cards for someone is a fun and gratifying project to do for kids all ages (including adults!).
The materials to use are very simple:
colored paper, use two different colors or more
scissors
tape or glue stick
stickers
pens or other writing/drawing material
Let the kids cut any shape from one paper and use tape or glue stick to attach to the other colored paper. Use stickers and pens to decorate the cards.
Note that using tape is a difficult task for little fingers, but I think it's very important for them to try out a lot by themselves. Offer some help if needed, but don't take over. Kids around the age of 2+ usually just want to pull the tape in very long strips, let them if you don't mind: they stop with it once they have learned what it does and move on to learn how to cut it off and use it in short strips.