You're welcome. You don't have to go through annulment first.
What you should do is to make a list of the expenses for your child.
Child support covers:
1) living expenses (such as shelter, food, clothing, diapers, etc),
2) educational expenses (such as tuition fee, school supplies, school uniform, etc), and
3) medical expenses (such as doctor's fees, hospitalization costs, medicine, etc).
Then, based on the list, compute the reasonable amount of support that the mother should provide for your child/children.
You can send a demand letter to the mother, stating in substance, the obligation of the mother to provide support, the expenses of the child/children, and the amount you are demanding as child support. You must also state the period of time you are giving the mother to comply or respond, otherwise you will take legal action.
If you are going to give the letter in person, give 1 copy to the mother and another copy to be signed "received" by her and the date received. You should keep the "received" copy.
If you will send it by courier, keep a copy of the letter and keep the proof of posting.
If you file for annulment, a prayer for child support while the case is pending an also be included.
For the cost, please send an email to km@kgmlegal.ph
I do not provide professional fee quote in this forum.
Best regards,
Atty. Katrina