Stinging nettle is a great herb for allergies and other health problems.  It's even edible!

One of the most difficult challenges a parent who wants to use herbal remedies faces with their kids is, “how do I get my child to to take it?”  While there are a number of tricks for getting children to use herbs, I find that the easiest and safest method of administering herbs to children is to make herbal glycerites.  This article contains instructions for making sealed simmer glycerites, a very easy-to-make, but effective herbal preparation for children (and adults).

In the early 1980s I worked with Master Herbalist Edward Milo Millet, helping him develop a Master Herbalist training program.  Millet introduced me to Samuel Thomson and it was Thomson's ideas that finally helped me understand the basic principles of natural healing.  This article is an introduction to Thomson and his healing work.

This article talks about using herbs with children, how to get over your fears about treating your own kids, how to calculate doses and how to administer herbs. 
In the Audio Recordings section, I've also uploaded a conference call about my favorite herbs for children.