An established tank is a must for Cardinal Shrimp. They seem very happy picking on rocks and the aquarium substrate. The only other foods, as a treat, my Cardinals will except are Bloodworms and tetracolor flake food. Be careful and do not over feed. Once they feel safe in their new environment, they will come out of hiding. Be very careful with any water changes. Cardinal shrimp are very delicate.
By the way, where did your mom find your Cardinals? I am always looking for new unrelated specimens to strengthen the gene pool of my colony.
Regards
Austex