The Child Exploitation and Online Protection Centre (Ceop) has said one in 12 children met up with someone encountered first online.
Online friends
The ID scheme was set up by UK businessman Alex Hewitt after he discovered that his daughter could only verify the age and identity of a third of her 150 online friends.
He said: "People want to feel safe online and know the people they are talking to are who they say they are."
The company said it would also use software techniques "similar to those used by the passport agency" to authenticate applications for the ID card.
The system can only work if two children messaging each other online have both signed up to the scheme.
Children swap their assigned NetID nicknames and take turns to log onto the service's website.
The IDs are confirmed only if both parties have entered their e-mail address and passwords into the service. The card costs £10 a year and Mr Hewitt said he hoped it would "substantially reduce" the risk of young children being targeted by adults.
Jim Gamble, chief executive of the Ceop Centre, said: "Any measure that can help identify the real age of someone online is one more step to deterring people from assuming different online identities to exploit, groom and abuse children over the internet."
Detective Chief Superintendent Tom Porter, head of interventions, of the Scottish Crime and Drug Enforcement Agency, said technology could not guarantee complete protection.
He said: "We would advise all parents and young people to remain vigilant to potential dangers and ensure no personally identifiable information is shared with online strangers."
