Observe them at a distance and see if a mama cat returns. Give her 8 hours. Their best chance of survival is with their mom, second best chance with an experienced kitten rescuer. Mama cat may have just gone to get food. 

 The mom's still with them. I gave them some water and some cat food, but I think they've been up there for a little while because the cat's eyes are open, if just barely. 

 Then continue observation at a distance. 
Mallory is correct. Patience is critical here 

(I foster abandoned kittens) 

 If you’re willing, keep feeding the mom. It will allow her to stay close. You could even see if she’s willing to move inside with them. She might move them to a warm spot with food and water readily available. 

 Unfortunately, she moved her kittens, I have no idea where she moved them to. 

 You might see them around in the future. She probably just moved them to keep them safe. 

 Adopt them all if you can 

 darn it I'm pretty sure that cat relocated her babies

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