I regularly address the issue of the far greater safety of herbal medicines compared to orthodox pharmaceuticals. However, I am always quick to remind people that herbal medicines are quite powerful and all medicines must be approached with due care.
This is especially so when children are involved. I repeat, take extra care when giving any medicines to children.
When dealing with pharmaceuticals it is common to find a clearly stated recommended pediatric dose. These are always much smaller than adult doses. There is often a graduated scale based either on age groups or the weight of the child.
Herbal medicines also should be given in reduced strengths to children. A graduated scale is provided in the Herb Health Guide under Suggested Doses for Children [1]. There is also a warning given to be aware of the possibility of an allergic reaction.
One important issue to remember when adjusting doses based on some starting strength is that the original strength must be known. That may seem like a perfectly ridiculous thing to suggest, since it is so obvious, but the starting strength may not be as well known as you imagine.
If the herb you are using is already prepared with a clearly stated strength, that's fine. But what if you made a decoction yourself? Perhaps you have made a calming herb tea for yourself for years and now you want to give some to a child. See the problem. You don't really know the actual strength of the herb in your usual tea.
My recommendation would be to avoid using herbal medicines for children when you cannot determine the starting strength, and therefore cannot determine a pediatric dose. It may well be that you can create a diluted strength following the guide mentioned above, but you would need to know the strength you are starting with first. The smaller the child, the more important this becomes.