I posted the original question some months ago, and thought I'd give an update. Since it's now a long time since my kids have had (or even seen) store-bought yoghurt, I find that they have forgotten what it is like. My DS10 now happily eats plain unsweetened yoghurt, or will also stir through jam or orange butter (TMX made). My DS7 only ever like vanilla yoghurt anyway. While I have tried him on sweetened homemade yoghurt, he wasn't a great fan, so I no longer try - I just put plain yoghurt into banana smoothies, fruit puree ice blocks and baking.