You can take oreganol in water, food whatever but with hommeopathics you take alone or in water.
It's because alot of absorption is carried out in the mouth. If you hold it under your tongue for as along as you can then this is being abosorbed straight into your blood stream quickly.
When taking homeopathics it is for the same reason but absorption is not being interrupted by acids, food etc. You take it away from foods, water etc so it can do its job. However, some have very sensitive systems and find that its less of a strain on their system if they take the homeopathics in water and sip it.
For a child taking oreganol putting it in food may be easier. I would be careful with that stuff as it is very strong.