Herbs sachets to keep in drawers or wardrobes can be a good idea for small kids, and they won't have oil stains on their clothes afterwards...... they love picking herbs. For the more skilled ones, they may also like the idea of gathering herbs AND sawing up the sachets from scrap- get a lot of colourful, flowery cloth and they will love it....
Or powders, if you want to use oils..... put some talc powder in a small plastic bag and mix together a few drops of oils to create a very personal powder...

Shake it well, but make sure the bag is closed tightly with an elastic band or it will look like you're just back from the flour mill.....
