This means both women in a couple can legally be the parents of children without going through complicated and expensive adoption procedures.
The same rules do not apply to male couples because legal parentship rests with the mother and she cannot simply transfer it, news agency ANP said.
Gay rights lobby group COC said at least 20 couples took advantage of the new rules and formally recognised their partners’ children on Tuesday.
There were special ceremonies in Nijmegen, Alkmaar, Den Haag, Wassenaar, Leiden and Zwolle, the COC said.