My kids are currently 2 1/2 and 3 1/2. Here are some crafts I've done with them in the past year. You can let the older kids simply be creative or you can give them more specific instuctions appropriate for their age.
Gluing pompoms - I gave one child the lid to a shallow box and the other the bottom of the box. We called them picture frames. They glued different colored and sized pompoms into the lid in random order. Then I attached a string and gave them to the grandmas who hung them on their walls. I also made snowflake shapes out of popsicle sticks and the kids glued white, blue and gray pompoms to them. In both instances I put a little bit of Elmer's glue on a plate so they could dip the pompoms into the glue. (Older kids could be asked to make a flower, rainbow, animal, etc.)
Stickers - We put spring themed stickers on plastic cups to use as vases for Easter flowers. (Older kids may be able to spell out their names or words with alphabet stickers.) Foam stickers are fun, but my youngest has only recently just learned how to peel off the backing without getting frustrated. As an alternative, they make foam shapes without the sticky backs that could be used with glue.
Painting - We painted small rocks to put in our garden. We've painted pictures on paper with watercolors and fingerpaints and we've used brushes, cottom swabs, cotton balls, sponges, etc.
Stampers - My kids love stampers. We make holiday signs, cards, etc. I recently found "rolling stampers" at a dollar store. They love how they can make a whole line of little stamped images. I buy kid-friendly ink pads with washable ink.
Caryola Color Wonder products - My kids (and older neices and nephews) are amazed at how the colors magically appear. They have finger paints that are nice because they are "no mess". I pull those out when they really want to finger paint but we have only a little bit of time or I can't supervise as closely as I would with regular paints.
Scratch Art - I found these on the Oriental Trading website. They are pieces of paperboard with a black, wax-like coating. You scratch off the black coating to reveal the colors underneath. They come with pointy scratching tools but you could also use popsicle sticks. We chose the heart shaped ones to use as valentines, but they come in a variety of shapes.
Play doh - My kids will play with this for hours. They love to be creative. They have a variety of "tools" to use.
Have fun!