I would be more upset with myself for not having transferred the photos out of the camera before something happened to the camera. You could have still had the camera and had it, I don't know, fall in the bathtub or stolen before having the pictures transferred. That's not his fault.
I would be upset about him having lost the camera and not having said anything as a separate issue, but chances are that since you have a second camera he didn't think it was a big deal. I'm guessing he didn't know what was on the lost camera? Or he wouldn't have been careless with it.
Also, not for nothing, but the only people who tend to think that the pregnant body is beautiful are people like us and our spouses. And our spouses only think that OUR specific pregnant bodies are beautiful, not other pregnant bodies, unless they happen to be an OB/GYN. :-) Kids finding the camera or anyone else were probably mortified and deleted the photos so I doubt that they're floating around.
So no, you're not really over-reacting but I think you're misplacing the blame about the photos.
EDITED TO ADD: It also sounds as if he thought he told you already. You've got people telling you to remain livid with him over not having told you and ooh, now there are trust issues and what else is he lying about or not telling you about... but what if he really did think he already told you?
It's not as if he can get the camera back, so are you expecting him to get as upset as you are? Do you want him groveling in constant abject apology? Do you expect him to have to pay for this for the rest of your relationship? Is this worth ruining your relationship over? I'm not sure what you wanted his reaction to be. Be upset, you're totally entitled to that and you need to work it out because you only just found out and are disappointed. I would be too. Just... when you calm down look at it objectively too.