So if you have pictures of all the daycare kids and a family leaves it can make it impossible to get rid of those pictures off the Internet.
As said, day care photos I do not tag with parents names. They can tag themselves and I will approved that but I will not approve the tagging of other family members, not will I approve the tagging of a photo which includes any one else's child.

Sure, that means someone can copy the photo but like you, I have a contract which covers this - I work as a photographer too and so there is a huge conflict on interest and that has to be covered by my contracts and also explained to day care parents.

If I have photos of a day care child and they leave, they are immediately untagged from any images they had tagged themselves in, and also removed from the group. It's current clients only. If they have copied the image, there's not much I can do about that - but my contracts do state they aren't to do that and so I suppose if it became an issue, I could pursue that matter if it was deemed serious enough.