You can start your child off onto the wonders of the internet as soon as he or she is old enough to read a bit and is able to effectively use the basics of the computer.
Yes there are many safety concerns about what is out there, however, before starting, you can put in place some basic rules for your child and safeguards on the computer.
And then there will be an entire world of knowledge and fascinating facts that open up to your child. They can be age specific and go a long way to actually educating your child and increasing his or her sum of knowledge.
To begin with, you can open an age appropriate site (explore it before hand to see that is it suitable and has no external links) for your child (you can permit your 5 year old to do this) and let him or her navigate and explore it.
Pick a site that uses games and interactive activities to involve your child. Perhaps you can pick one that has some favorite cartoon or TV characters involved in a vocabulary game or one that helps your child increase their level of literacy.
Make sure you start out slow, that you limit access and that there are other interesting activities as well so that the child does not form an early or unhealthy attachment to the internet. [internet safety tips]