(Edited for clarification since my original post was confusing, badly written and implied things I did not intend)
Thanks guys. Don't worry I will continue to honor the agreement and not post the portraits, as I have all these years. It was something I had always just wondered about and wanted to talk about with people with a fresh perspective. I think I wrote my original post in an unclear way - from the start, I personally thought it would be unethical to add them to my portfolio. I did think it was a little unfair, but if something is agreed upon you stick to it whether it is fair or not. Since the agreement was made on such informal terms, I had been told by different people that it wouldn't be unethical, but it didn't feel quite right to me so I wanted to check with more people. Now I know for sure that it is unethical, as I first thought.
I respect the commissioner's wishes but was I originally wanted to know if the time that had passed and the older ages of the portrait subjects made it ethical to now post the images (I think I didn't make this clear at all in my OP), since the children are older now I imagine the safety issue wouldn't be a concern anymore (I'd imagine not showing them when they were still young was for safety reasons. I should have instead titled this, "Is it still unethical to post the images," and I know now that the time passed and ages do not matter and it would still be unethical because I wasn't clear with the terms (and also as Vineris said the children still have a right to their image even if they're older, and would need model release forms. This I did not know. I am still inexperienced). Even it was a hazy agreement, everyone is right that it is too long ago for it to be even worth it to do someone that may be against the commissioner's wishes. Even if I was too young to know at the time, it was still up to me to define them since I was the artist, and it was my mistake and an experience I learned from.
Second, my complaints (like when I said "I don't think it's unfair to include just one portrait in my portfolio" as Mute quotes below) had more to do with the "unfairness," not the ethics. I was complaining that the situation felt unfair to me, but that didn't mean I was going to compromise my ethics and go ahead and include the portrait just because it felt unfair. I feel so guilty if people thought that's what I meant. I didn't mean that at all. I was complaining just to express my frustration, I should not have done so. As I wrote above, I was only wondering if people here thought it would no longer be unethical due to the time that has passed and the older ages of the portrait subjects, which I now know makes no difference). I chose my words poorly. I was verbalizing my frustrations from remembering this event which I hadn't thought about in a long time, and I shouldn't have let the memory upset me. I didn't mean for the tone of my posts to imply that I didn't respect this commissioner and was going to add the images to the portfolio anyway. And even if I thought it was unfair, I only felt this toward the situation, not to the commissioner or portrait subjects, I truly wish nothing but the best for them. I was as polite and nice as I could be to the commissioner in person, even if I was nervous.
And though it is arguably "unfair" that I cannot post them anywhere (from my perspective, a third party might not see it as unfair to me at all, since it was ultimately my mistake and my responsibility as the artist to set the terms), not posting them is the ethical thing to do so whatever feelings I have about fairness do not matter, and why I have been honoring the agreement. I will not and have never posted them anywhere, just to be clear if it wasn't from my original post. Which was written when I was a little delirious from sleep deprivation and work stress and where the colorful/hyperactive language came from, I am sorry.
I responded to everyone in a reply that will be posted soon.
Thanks again, I appreciate the time you all gave to share your thoughts.
I'll get back to drawing now.