Children were born in thailand and have dual citizenship they were married in Sweden been together 8 years, he said he was taking them for a holiday, and now he won't bring them back . Any suggestions on what she should do next,

go to the swedish embassy and report what has happened,maybe they can help

When the situation is reversed the quickest action which may have good results is offer money for the kids return. Seriously, A quick trip to Sweden embassy should get answers which are somewhat accurate vs TV. Take all supporting documents, marriage, birth certificates, permission to travel for them to leave with father initially, etc and she should get some real help and support.

Who has custody?

Where did he take the children?

Swedish newspapers love stories like this, contact Aftonbladet.

Bureaucrats won't do anything unless it gets some headlines.

As said, contacting the Swedish embassy is a first and see what adivise they give.

But right now they are married and both parents hold custody over the children, it might be necesarry to file for a divorce and custody over the children.

First off all think about the kids, and don't be selfish. The kids will get a better education and life in Sweden than Thailand.

Children were born in thailand and have dual citizenship they were married in Sweden been together 8 years, he said he was taking them for a holiday, and now he won't bring them back . Any suggestions on what she should do next,

Yes, Get a someone who can articulate the details more clearly...

Is 'She' Thai and 'He' Swedish ? Did they get married in Sweden and move to Thailand where they lived together for 8 years ? Where are they now?

From the information you have given - They are still married, kids have dual nationality and they remain with a legal (Parental) guardian.

The information is sparse.

One could setup a website which automatically opened a thread on thaivisa in the apprioriate forum, and sell the service as personal legal/visa/etc/ counselling for $300 per question. Maybe we've found such a site!

The Swedish guy left with his children for holidays and won't come back?

What about his belongings in Thailand? And the ones of the children? I guess he did not leave for holidays with a container.

One could setup a website which automatically opened a thread on thaivisa in the apprioriate forum, and sell the service as personal legal/visa/etc/ counselling for $300 per question. Maybe we've found such a site!

Sounds like a personal get rich quick scheme to me.