This information is posted on the Dutch Consulate web site:
FAQ's
* My child needs a Dutch passport but I have no contact with the father. What do I do?
o If the father is on the birth certificate, you do need the consent of the father.
o If the father is not on the birth certificate, then only the mother's signature is required.
o If the father is on the birth certificate but you have sole custody over the child, a court order - carrying proof of legalization (e.g. apostille) - stating that you have sole custody over the child will be required. In the latter case only the mother's signature will be required.
* I need to give my consent for my child to get a Dutch passport but I do not live in the same country as my child. What should I do?
o Go to the nearest Dutch embassy or consulate with your passport and full name, date and place of birth of your child. You can fill out a form of consent over there that will be forwarded to the appropriate Embassy or Consulate.
o If you live in The Netherlands you can sign a form of consent at city hall ('gemeentehuis' of 'stadsdeelkantoor').
It seems I need not worry about him trying to get passports for the kids after all.
I intend to make phone calls verifying, but I think I can breathe again!