As a parent, and an IT professional, I've been concerned about giving my kids their own e-mail accounts. For me, it is mainly the concern that inappropriate content may slip by spam filters, but many people are worried about what types of communications their kids may be having with friends.
A great solution is zoobuh.com. They offer spam filtered webmail accounts for one dollar a month. But the real sell here is that parents can screen all incoming and outgoing mail before it is delivered. This way, you can be sure that the mail coming in is appropriate, and that little Billy isn't telling grandma that daddy thinks she smells funny.
The web interface for the child can be scaled up or down based on the child's ability level, and there are a few different "fun" skins to choose from.
It is the best price/value mix I've seen for this type of service. Since they offer a free 30 day trial, they are definitely worth a look.