Yes, I believe that childhood memories are good, because they return some people to a better time in their life. When people are having a hard time in life, it is greatly beneficial to focus on something positive.Whether it's past, or present. Childhood memories are a perfect avenue for this.
This question is impossible to answer objectively and with an unequivocal yes or no, it depends entirely on whose memories you're talking about. Some memories are of the sort that build character, like remembering a challenge you faced once, and using your success as inspiration to spur you on to greater achievement later in life. Some memories are of the sort that build empathy, like moments when it was shown to you, or when you bore witness to it being shared between others. And some memories are the sort that traumatize you for life, such as moments of abuse, neglect, fear, hate, or pain. The only reason I'm able to answer "Yes" here, is that, even the saddest, darkest memories have a glimmer of promise for the individual, that they might take whatever awful experience they have a memory of, and use it to be a better person themselves. Someone who remembers being abused as a child could use that memory to be resolved to only ever be loving and tender to those they hold dear. Someone who remembers being fearful of a thing as a child could use that memory to help other children deal with having the same fear, and perhaps make their lives better as a result. Someone who remembers being naively hateful to another person or group of people could potentially use that memory, and their growth since it was formed, to help others overcome their hatred and accept others. So, yes, childhood memories are more good than not good, overall.