Is it possible to insure a child under 18 years?


Yes, of course. The insurance is made by the parents on behalf of the child.
Yes. Lots of people do it.
Yes, as young as 1 year old for the Health Insurance, life insurance...

If you want to check the quote for them;

Health: http://www.insureme.com/landing.aspx?ref...

Life:
http://www.insureme.com/landing.aspx?ref...

You will have several quotes within a few hours later. Then, you can choose it
anyone any age

Answers:

Yep... haven't you seen those commercials for Gerber Life Insurance?
You don't say what type of insurance, but yes, you can - life, health, auto. There are some good life ins. plans for kids under 18, if this is the type you need. They can be insured at a very low cost and then be guaranteed life insurance when it matures, regardless of health at that time.