HELP!!! Found baby birds in yard ?

help.... i was in my house with my mom i am 12, and well my mom saw these boys in our yard hitting something with a sitck (a large stick) and well she walked out there and she saw a nest and when she asked what are you boys doing one of the boys ran off and the other one just shrugged his shoulderes and left. then she walked out to the end of the yard and there sitting on the ground was a nest and four baby birds almost newborn but not quite all lying on the ground litteraly shaking so we put them back in their nest and took them inside and put them under a lamp and mixed cat food and water and fed them a bit. so i needed help on what to do next we are about to put them back on the branch back where the nest was and see if the mamma bird comes back......... and if she doesnt please help me and tell me what t do next!!!!