/altnature.com/library/kids.htmThis woman grinds the dried herbs in a coffee grinder and then mixes the herbs with nut butters. That surely might work. However, you have already bought the tinctures.
I have taken my tinctures quickly in water and then immediately eaten. So I wonder if mixing the tincture in a mild smoothie would negate the effect of the herbs. I think just a banana and some yogurt and the tincture might be worth a try.
I bet if you call Sage Woman Herbs in Colorado they might be able to tell you how to get a child to take a tincture. They are the most helpful people. Or if you have a local herbalist or herb store you could ask them. And please let me know what they say!!! I am so curious.