Yeesh... technically, if there's nothing in the pic to enable a geographic pin-point, then theoretically there's nothing wrong with it, but... I won't.

I set up a server with SSL and I only let them be seen by those granted a password... but maybe that's just me and because I'm too selfish, or something... I dunno.

As long as the children arent' identified. From the picture above, I have no clue where or who, there seems to be no harm done.

http://farm3.static.flickr.com/2338/2474224640_acfaaed6b0.jpg

You may be aware that most schools will not post pictures, names, or any other information on-line without the permission of the parents. Here is a quote from a typical policy on the matter:

"Parents have the right to approve, disapprove, or revoke a previously granted right to post a student's picture or other personally identifiable information".

http://www.mcs.k12.ny.us/privacy_policy.htm

Do you really have the right to take pictures of other people's children without their permission and then give away the rights to publish those pictures to everyone in the world, again without permission of the parents? I don't think so. Even if it turns out I am wrong and you aren't violating any law, doesn't it just make sense for you to secure the permission of the parents? For all you know you may be photographing a child of a battered woman who is being stalked by an ex who will kill her or kidnap her if he can find her. And I hope you don't think those men aren't spending countless hours scouring the internet for any hint they might find. I admit this is unlikely, but people are injured and killed in unlikely scenarios quite regularly.

I'm also thinking that not many people would be as nonchalant as some when it comes to posting world-wide reproduction rights to photos of their children. I suspect that would make a number of people uneasy.

If I were you, I would ask them right at the time you take the photo. Give them an ID card with your name, number and website address, and ask them this "I'm taking pictures of my kids playing. I notice your kids are in some of the photos. Is it all right if I post them on my internet site? If you don't like them or change your mind, let me know and I'll remove them." If they say yes and you want to go further and ask permission to post them to flicker or wiki commons for the whole world to reproduce, I think you should ask them. Can you even imagine finding pictures of YOUR children posted on line by surprise? Pictures that you didn't know existed, and sure don't know how they got on a particular web site?

Carry a little note book to notate when and where you received verbal permission, and from whom.

Image recognition software is becoming more advanced all the time. Is it really far fetched to think that photographs will soon be search-able by providing a source photo as a search term? In fact TinEye is already doing something very close to that, as is LTU (see sources below).

Apart from safety concerns, parents are concerned with making decisions for their child now, that will affect their child's ability to make privacy decisions later. For example, if tell you sure, go ahead and give the whole world the rights to my kids photo, haven't I more or less excluded him from that decision? When he is older, and perhaps develops into a rather private person who doesn't want to have his picture distributed all over the internet, shouldn't I perhaps have reserved that decision for him? If I as a parent make it a general rule to reserve the rights to post pictures of my children, I can take the pictures down or protect them whenever it seems appropriate to me and/or my child. If, on the other hand, if I've given you and the rest of the world rights to those pictures....

I kinda liked this video, as it touched on some of these points from sort of a blogging parents point of view:
http://www.youtube.com/watch?v=cd2p8_OXtfw

Although it may not seem to be a big deal to post pictures of other people's children playing with your own online, always remember that schools or child care centers typically require parents to sign a photo release form before children's pictures can appear in newsletters, on bulletin walls, on websites, or for display in classrooms. You could avoid the trouble of contacting the parents of children in photos after-the-fact if you get their permission to photograph their children beforehand and inform them of your possible intention to post some of these photos to online websites.

I don't think it is right to put someone else's children on the internet. I don't want my children's picture on the internet anywhere. I refuse it when asked through the school and if you had a picture of my kids playing with your kids I would be very angry if you posted it.

I rarely post my own grandchildren's pictures online, and would never post the pics of anyone else's children without asking their parents first. If the kids are all grown up now, that might be a different matter. I'd probably still ask their permission before posting their childhood photos, if I knew where they were. If not, and I thought I just had to share the photos online for some particular reason, I probably would, but take them back down again if the grown-up child contacted me and asked me to. One really isn't supposed to post pictures of people, even strangers, without their permission.