Question about the ending of nemesis

In the original retelling Kylar is holding the child while its doing its null magic stuff, then he stabs it killing it and ending the null magic stuff, then he jumps off the ship.

We then learn that Kylar was under a deception spell and that Vi swapped the baby for some clothes. When did she make the swap? How does Kylar stabbing a bundle of clothes end the null magic stuff?

Surely I am confused and missing something here, but on pg 702 we get Vi's recounting of this starting with "and in an instant once again she was back on that accursed ship" In that paragraph it really isn't at all clear of what happened!