How to teach a child to type?

My recommendation would be to look at the curriculum of your child's school and go along with that. If the child is typing on their own already, then just letting them see you touch type and telling them what you are doing -- rather than what the child should be doing -- is a good way to introduce the idea. Actually, that's a good way to introduce the idea regardless.

Anyway, although a child's developmental age can vary greatly from their chronological age, in general, ten seems a bit young to me for learning the skill unless the child already has a specific direct interest in touch typing or an interest in something that already has them banging on a keyboard to write.

Good luck.