Ethereum and litecoin are good if you are buying with little money.. They are growing steadily and i think will be good future investments.

At any age you feel your child has the ability to understand it. Just teach her/him in bits and eventually show her the sites and how to go about it.

Ethereum is moving at a good pace but i highly doubt it would get to bitcoin or surpass it.. But then again, nobody ever thought bitcoin would get to where it is now, so at this point i prefer to say anything is possible.