Probably would be a lot simpler just to sprout things for them. Get a big jar, like a one gallon plastic jar with lid, poke some small holes in the lid to allow water to drain. Put about 1/4 cup of a sprouting seed in the bottom, such as alfalfa, wheat berries, radish, whatever you think they would like. Pour enough water over it to cover, and let sit for about 6 hours. Rinse and drain. 3-4 times a day, pour water over them and then rinse and drain. For very fine seeds like alfalfa, put some fine mesh inside the lid so the seeds don't come out the holes. Set the jar in a warm, bright spot. Sprouts will be big enough to feed in 3 to 10 days, depending upon what you're sprouting. They'll love it. Cheap and easy if you stick with bulk, non treated seeds from the feed store -- you can sprout almost any kind of birdseed this way.