Don't be too worried about it. All your deleted photo and videos are possible to be recovered.The reason why they are lost from your SD card may have something to do with the battery change by your husband. He might not operate it in a proper procedure like change the battery without close "Power Off" button or similar situations. Maing your taken photos and videos didn't well stored in the card thus lost.
Whatever happened, I don't think there are some problems with your sd card. But the most important thing is you can try some photo recovery software to get your lost photos and videos back. Here is the Top 6 Free Photo Recovery Software for your choices.
However, freeware are usually less powerful than commercial ones. As these photos and videos are so important to you. I'd like to recommend you to try a nice program called Wondershare Photo Recovery. This one offers free trial version can deep scan SD card to find the lost photos and videos. Once found you can also preview them to see if your lost ones are listed there and then pay to perform full recovery.
Good luck and best regards
We took a ton of photos & video today at Rolling Thunder, DC. When I went to put them in my computer, only a few from the end of the day were there. We have no idea what happened. The only thing I can think of was my husband changed the battery around the time of day where the pictures were deleted, but I don't know why that would have deleted all the photos/video (and there was a ton there). I wish I knew how this happened, and we're both so upset.
I've been reading about photo recovery programs. Do these work & can you recommend one? Preferrably one that's not too expensive or has a free download?
Any ideas how this happened so we don't run into this problem again? Wondering if this sd card is somehow responsible and maybe we shouldn't use it again?