Here are
some threads to get you started. I think anything goes which tends to show intelligence and/or advancement. If it is work or creative output of some type, it should be made without adult help. It doesn't have to be tangible; if I recall correctly, I've seen discussion here of recordings of children performing or doing math problems, or even just discussing topics of interest to them. I think I'd err on the side of including more information than you think necessary, but that's just me; I'm sure a single portfolio item could be compelling enough.
EDIT: I float in cyberspace corrected. See the actually informative post below. I don't know how I forgot the need for 3 items.
