My suggestion is fabric Christmas ornaments, personalized to reflect their preferred colors or themes. I am suggesting this despite their young ages because I still treasure the ornaments made by a dear family friend for my brother and me when we were small. Maybe I am a sentimental softie, but I still smile (and tear up) when I unpack the ornaments each year and see them again. ('Course, the fact that I have both my own and my brother's ornaments tells you how much of an impact they had on him...)
Alison