Pablo,
I am pretty much in the same situation as you. Wife took my young son under the pretext of going for vacation and now refuses any sort of communication--it's been 6 months. All the advice I've gotten had one thing in common--get a lawyer to handle your Hague Case. I don't know about Argentina, but the lawyer I retained in Korea has been very helpful and informative. I tried going through the US State Department, but their role is limited to just sending in the Hague Application to Korea's Central Authority. The problem is the Central Authority just tries to talk to the abducting spouse and if they're unreasonable and refuse to cooperate, there's little else the Central Authority can or will do. Of course, mediation is the best solution, but for me, my wife won't budge and won't be reasonable. Retaining a lawyer is definitely recommended based on my experience so far.
I've lost my one and only son so I can't imagine losing three beautiful and precious children. God speed to both of us and I pray we see our children soon. Be strong my friend.