出生证和结婚证认证问题

我去荷兰做博士后，老婆孩子一起去。材料寄给秘书后，给我回了一封信，说是儿子的出生证和我的结婚证需要权威部门认证，我想问一下这是指的“双认证”吗？
具体应该到哪个部门去呢？

回信如下：

Today I've been called by the IND. They have told me that they can't accept the birth certificate of your son and your marriage certificate.
You have to legalize this documents by the authorities in your country.
After that the foreign diplomatic missions have to give their permission too.
I don't know how to arrange that in China so you have to look for information by your self on the Internet.

证明要先拿到公证处做公证，然后送到外事办去办双认证。有的城市的公证处是可以代办双认证的，你可以先问下公证处。

外事办？
是市政府的外事办吗？

http://www.fmprc.gov.cn/chn/pds/fw/lsfw/lsrzjzwslggz/t312468.htm

Yes, you need do lieagulization for your certificate. Here is the information for all the agency, you can choose one is closeto you!! they will help you do base on your certificate documents which you sent to IND I think.

为什么不能在中国大使馆办理呢？