I bought three of these, one for each of my grandnephews and niece, who are each six years old.  Two of the children paid it no mind, but one of the boys, who loves to read and assemble all sorts of things, put it together in one afternoon while he was at his grandmother's house, and now he displays it in his room, alongside his other model kits.  I sent each smart lab with a few anatomy books for children, which included information on the heart, stomach, and ears.  The little studious guy enjoyed everything.  The other two children enjoy more physical activities, e.g. helping grandpa in the garden, so they weren't ready for this.