That sounds like Jane - seemingly unable/unwilling to receive any support/comfort. I tried for years to help her, to listen, be nice, etc, etc. For some reason the first time she accepted my attempt to help/soothe her was after she talked to our T a few times. She told him her feelings of hopelessness/disgust/etc, and his response was incredibly compassionate/understanding/gentle, which confused her and made me want to cry. But then she accepted my comfort the last time she had flashbacks

...
I don't know how it 'worked'. Do you have a T you can talk to?
You can't make them happy. They can't make themselves happy. But you can validate their suffering. They probably have no reason to be happy right now; healing takes a lot of time. (ninchen went from a mute and paralyzed, terrified child, to a 'normal' one - sometimes happy and excited and playful, and other times sad or scared, etc - but it took about three years of trauma work.. Jane said the word 'hope' for the first time

. Change is possible!)
Good luck. I know how frustrating it can be to have littles you can't soothe/help...
Do you know what may have triggered them? You wrote that they're not always unhappy.