Get some netting or hardware cloth to put over the top and start working your way down the sides with some more. At least you wont' need to worry about the floor since it's concrete. If it's big enough maybe get some pallets and build them a simple shelter for now within it where they can snuggle down is hay or straw and sleep and you won't have to worry about predators getting them.
Can you post a picture of your kennel? This is what I recently made in my run for some of my ducks just to give them shelter from the rain, wind and sun during the day and they love it. It cost me nothing and took no time at all to make. The hardest part was lifting up the pallett for the top by myself!
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