Hi Xjw,
My cousin went through something similar in California, but her jerk-x is a muslim and took the kids out of the country. I think you will have a better outcome than her though, since your X is american. My cousin has her kids back but it took a long time, and the son is completely brainwashed.
I hope you can track her down and the kids too. Did you try contacting the kids school to see where their transcripts were forwarded to? Usually the schools won't just let you take the kids out without knowing where they are going. But California is so overburdened, they may have skipped that.
The thing that got my cousin back her children was that the X couldn't prove that the kids were legally enrolled in school when he finally brought them back to California. Also, he wasn't taking the children for medical appointments to treat chronic health issues like asthma and allergies. That is why she got the kids back.
I'm glad you have an attorney and you are getting help. Is it possible that something completely unrelated to you has occured with your X? For a woman to leave her home, generally means she did not feel safe being there. Could someone in her apartment building have been harrassing her and making her scared or maybe someone at work or a wacko from the internet?
My thoughts and prayers go out to you and your children.
Chrystal