We even have to have the consent of other adults now, before sharing any photo they are in.
Regarding children, from what I have read, at the very least, a picture of a cute (healthy) baby or toddler could be copied and circulated with a false name and a request for funds to pay for an operation or treatment to save the child’s life.
At worst the picture could be used by a paedophile in a variety of ways. For example, on facebook, pictures of a child taken together with other information from the poster - if they do not have rigid security settings and/or from clues in the background of the picture, - can indicate where they live, which school they go to etc and a paedophile can from there befriend the child on the way home from school or in the park/town etc by appearing as a friend of the family, knowing their name and other things about them. From there, anything can happen, from grooming to kidnap. Even if the original poster of the picture is careful, once the picture is online, any ‘friend’ can repost it and it could end up anywhere. It could be used as an ad to draw people into a ‘dating’ agency. Given the easy availabilty of programmes that doctor pictures, a photo could be used in a manner that places the child in an apparently embarrasing situation. Unfortunately it may be a young teen posting a picture themselves who ends up being compromised.