I used to have a nice picture bible growing up and I read and re-read Revelations growing up as a kid. I recently heard that verse but it's not as I remember it. Did it always say "or in the hand?" or just forehead?
BibleGateway.com has about fifty English translations of this verse, and they all include hand.
This includes older translations like the KJV, RSV, and The Living Bible (1971). Of course, Bible Gateway is not exhaustive, so it's possible that you had a children's Bible using a different translation or paraphrase.
That said, it's clear that the inclusion of hand in this passage is not a recent development.