Hello FadedLily, From your description it sounds like your little family "thinks" something is blocking their path so they are unable to go up or down the stairs to/from the 2nd level, especially since your little person was able to clean a dirt smudge but then not come down the stairs. Try the tips linked in this post and see if they help. Furniture near the stairs, even if it's on the other side of the wall, can sometimes cause issues as described in this post and follow-up response. Please let us know if this solves the issue for you.