So, this is the first place google dropped me off at... I even went through the exercise of reloading stock firmware and going through all the updates, formatting my SD card and then loading the videos anew onto my SD card... And after doing that all the video content was accessible for me to let my kid see them in Kids Mode! So I then go about downloading their other apps and before calling it a night I check everything once... go into Kids Media Player and nothing... drop into the parental control section and it too refuses to show me any videos to select for my kid... drop out of kids mode into to regular launcher and I can see everything in the stock video app...
So somewhere between having placed all updates, and making sure the videos worked, and then downloading new apps... kids mode has decided it does not want to see what is on my SD card for video/media purposes.
I am hoping someone has found an answer. (as a side note, my other daughter has the exact same tablet set up with all apps running on it... and there has been no issue at all with her seeing all her videos while in kids mode...)