This poem reminds me a lot of Jungian psychology, specifically his archetypes. One of his common archetypes was the child, the eternal innocent who lives in a paradise of potential, which definitely sounds like the inner child and the sandbox you're describing. Part of psychology is development, but that also requires remembering and learning from past events and self forms. 'Sifting through memories' and 'I hold her, remember' speak to me of these things. You've crafted a very Jungian poem here, I dunno if that was your intent, but you did it and I enjoyed it very much.
At first I though this is just a good poem..But when I read it again, wow....the simplicity with which you have expressed your ideas is awesome...keep up the good work...I am also a beginner in poetry..If you find time , please review my poems too...