I don't know if they've changed it, but I remember seeing an Identakid card back about 10 years ago or so. It had one little id-card size picture of the kids face (maybe 1"x1") and one fingerprint. Just about as basic as one can get.

If something happened to my kid(s) I would sure as **** give them something a bit more than a 1 inch square picture and a single fingerprint. I'd give whatever I had that could help. If I've got detailed face pictures, full body pictures, a full set of fingerprints, their latest height and weight, pictures with them wearing the same clothing they were wearing when they disappeared, ect.......they're getting it.

If anything, I think it would probably be better to carry around a multiple good wallet size photos with descriptive information written on the back (name, age, size, weight, ect). That way, you can hand them out to the first officers or search personnel on scene and they can get right to looking for your kid. The faster they can get to looking for him/her, the better.