I work with children and every kid I've seen (mostly younger but older kids, too,) reading the David books like them a lot. They giggle when they see his bare bottom but don't dwell on it. I would have kids five years and up read them because they will understand that his behavior is naughty and "not allowed".
David and my 3 years old are so alike, reading the story and finishing up by kissing and hugging each one of my kids as David's mom does is a fun game for us. We read it often