I must admit, my own favourite work of Jansson's happens to be an adult one, the bleakly beautiful short story "Taking Leave". But her style strikes me as much the same, lucid and unfussy, whether she is writing for children or adults, and I doubt she ever made a difference between them in her own mind. We didn't have her children's books around because my daughter was terrified of Moomins, but I might revisit them now...