I honestly don't understand how my almost 8 month old sleeps through the night but my 3 year old…

I honestly don't understand how my almost 8 month old sleeps through the night but my 3 year old gets up at least 3 to 4 times a night crying and wanting either me or her dad knowing she's going to be redirected back to bed . . Please lord give me strength tonight so I can get through tomorrow.