Often, my children were doubting God, they were doubting because it didn't seem like He was answering prayer, or because other Christians had hurt or disappointed our family or acted without integrity or one of their friends had fallen from faith or adopted an immoral lifestyle. There are many reasons in a world full of temptation, but I think staying close, communicating love, affirming and understanding their questions and speaking forward into their lives is helpful. And of course, pray, pray, pray!