Baby birds in nest... no mother?

there is a nest at the bottom of my deck... its up high... there has been a mother in it for a while. but yesterday i looked... no mother... then again today no mother... and ive checked a couple times within the last 4 hours... no mother... will she come back? i have a cat who kills a lot of birds in my yard... i... show more there is a nest at the bottom of my deck... its up high... there has been a mother in it for a while. but yesterday i looked... no mother... then again today no mother... and ive checked a couple times within the last 4 hours... no mother... will she come back? i have a cat who kills a lot of birds in my yard... i am worried he got the mother. im not sure though. im not sure what kind it was but it was small... gray... and looked to have a long tail when it was there. i stayed far away so i wouldnt scare her.

should i try taking the next down and feeding it some moist cat food or something? i was reading not to feed water and its a good thing to feed cat food. if i leave them till tomorrow do you think they will still be alive?
i took a mirror to see if they were alive... they are tiny... with big closed eyes... little gray fuzzy feathers... and pink skin... they are breathing a little.

i dont know what to do... any advise please let me know
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