I'm a US citizen and filed I-30 petition for my sibling in Philippines back May 2013. I have new niece and nephew, Do I need to file I-30 again?

No. You cannot directly petition for a niece or nephew. The spouse and children of your sibling will be able to derive an immigrant visa from the petition you already filed. You may wish to notify USCIS of the birth of the children. You can read more about family immigration at http://myattorneyusa.com/family-immigration.