Parameters are accessed with C4DAtom::GetParameter()/ C4DAtom::SetParameter(). See Parameter IDs.
Parameter: Children
COMP3DTAG_CHILDREN
Parameter: Cache
COMP3DTAG_CACHE
Parameter: Anchor Point
COMP3DTAG_MIDPOINT
Parameter: Solid
COMP3DTAG_SOLID
Parameter: Size X
COMP3DTAG_SIZEX
Parameter: Size Y
COMP3DTAG_SIZEY
Parameter: Color
COMP3DTAG_COLOR