There are really two questions here. Can and will this affect our children's mental health and will this lead to our children later experiencing an MLC themselves?
These are just my opinions based on what I think I know about MLC.
First, yes this can and will affect our children no matter how old they are. My daughters were 31 and 34 and my granddaughter was 13 at BD and they've all been affected. I think the following three things are critical. First, they need to understand what's happening and to know and believe that it's not about them. Second, they need to receive and feel love and support. Third, they need to be able to talk through and work through their feelings about what's happening and how it's affecting them. If they're sad, they need to be able to cry. If they're mad, they need to be able to express anger. And they need to know that it's ok to experience those feelings.
Will they eventually experience an MLC? Children are extremely vulnerable during early childhood. Their brains are undergoing a tremendous amount of change during their first five years and during this time high, continuous levels of stress or traumatic events can affect the physical, structural development of the brain in ways that will greatly increase the odds of them later having an MLC. That certainly sounds like what they experience during an MLC, doesn't it? But it's still not guaranteed that it's going to cause them to have issues later in life. The real issue is whether they were able to develop a secure attachment during that period. If, during this time, the child is able to develop a secure attachment to just one person it acts like an inoculation against later problems with PTSD and other dissociative disorders that I believe are the basis for MLC. Are older children susceptible to later going through an MLC? If they get the kind of support I mentioned above, I don't think so. Even if they don't, I think it's possible but not likely unless the trauma they experience during the MLC is severe, ongoing, and ignored.
I'll use my situation for illustration. My father was a rageaholic, probably because of untreated wartime PTSD. His raging episodes were highly traumatic and set the stage. But what guaranteed my future issues with PTSD, anxiety, and depression was that my mother was raised in a household with an alcoholic father and as a result never learned how to be nurturing. She was emotionally closed off her whole life so I never developed a secure attachment with anyone when I was young. I had nobody to go to during my father's raging and nobody to talk to about it and to help me understand it or to soothe me. In fact, I think one of the reasons I'm having such a hard time with my wife's MLC is that she is the first and only person with whom I've ever developed a secure attachment. When I lost her I lost the foundation my life had been built upon. I'm still floundering without her.
I hope something in here has been helpful. I truly believe that one person can make a huge difference. You can be that person.