I, too, memorized this poem in school and was touched by it's poignancy. I have a friend who lost her son to a brain tumor and it also touches her in a special way. I don't think that the child in the poem died in his sleep, but he has grown and moved on and, and sadly, the time of his playing with toys has passed. I think it speaks to the fleeting time of childhood, and the bittersweet combination of fond memory and the reality of not being able to stay at that point in life. Either way one sees the poem provokes a very emotional response. The beauty of poetry is that it can have several interpretations and neither is "wrong."