If you actually try it.
If. What does if mean?
actually. What does actually mean?
Actually means really. But what does really mean? genuinely. But what does genuinely mean? actually... 
How do you explain what words mean to a child when you have to use words that mean what you are trying to describe and they don't know what they mean either?
To describe a word - they have to know the word, or the concept, or another word that means the same thing, don't they?
You can teach words that name things. That's easy. Point to the sofa and say "sofa". But apart from names of things?
It just goes to show how much we take language for granted. Most children just absorb it. Having to teach it is hard!
Anyone come across any good books?
Slap for the first person to suggest thesaurus