Its called night fright, very commm in tiels. They catch a bit of light from somewhere and it scares them it is perfictly normal. I have had them even fall out of the cage. Be patient you have only had them for a few days. Coax them out with foos that they like, mine like wheat thins, rattle the box and there on top of my head. Start with baby steps, they will warm up to you soon.