There are two parts to this post. It's all about introducing in small steps with 3 & 4 year olds. This was my end goal (of course found on Pinterest) - but how would I get there?
Step One: Get the rice from a Wholesale Club of some kind. Cheapest and easiest. Don't worry about quality, you won't be eating it, it's just to play with.
Step Two: Colour the rice. We used baggies. Put in a 3 or 4 cups of rice, added a few squirts of hand sanitizer and a few drops of food colouring. Mix it all together. Depending on how dark you want the rice, you will have to play with the amounts. Then we dumped it out to dry. It doesn't take that long to dry.
Step Three: Let the children play with JUST the rice for a few days (or weeks). The kids loved playing with the rice. We gave them small shovels, strainers and we made some larger funnels out of construction paper.
Step Four: Add the letters. We actually had to add more rice to the table because A. Lots was dropped on the ground in two weeks and B. We wanted the letters to be hidden and LITTLE harder to find. I used the ABC Foam Puzzles that we have in the classroom and just put the puzzle base on the table beside the rice table. My daughters Kindergarten class also had this in their classroom and she put the rice table right beside the whiteboard and used magnetic ABC's to match under the hand written ABC's on the whiteboard. Two different possibilities!