Why Doesnt Prayer Work?

Why doesnt God hear us who pray? Why aren't the sick always healed. I am having a semi- faith crisis. I am very sad for a family who has had a lot of people praying and their child is only getting sicker. I am sad for another family I prayed for and their child died. Why? If God answers us who ask....then why? If anyone can help me with this very important question, it would be appreciated. Thank you, just having a  rough day.