The Internet is an open community. Just like your hometown, there are places you want your kids to hang out and there are people and places you want to protect them from. The scariest situation imaginable is a child who turns up missing or is molested as a result of an online meeting. A child is just as likely to run into harassing, belligerent or demeaning messages in Email or Internet discussion forums as they are anywhere.
Children have a right to privacy.
Their name, age, what school they go, is their business and the business of their families. No one, including reputable companies, have a right to extract this information from children without first checking with the child's parents. It's even possible to find places on the Internet where you can learn to make bombs or other weapons. Children can sometimes be tricked into giving out passwords to Internet services or credit card numbers. Sometimes they just like to experiment.