This was a hardback picture book we read in the library in the 1980s. Two or three children go to a fair. On the way to or at the fair they get some small items (possibly a gold star?), which are put in a ‘cornucopia’. I think this was pictured as a paper cone. On the way home through the forest, robbers steal their treasures. I think it had the line ‘what wicked robbers to steal such precious things’, the point being these are items of no commercial value, but things of wonder to the children.
Is it the Three Robbers? It was my husband’s favourite story to read to our kids
Good Luck!