It sounds a bit experimental - but if he really wants them, and isn't just doing it for a power struggle, then why not. It may be that the boys will want to return to her after a while and make that very clear. Maybe she would like a breather from being a single parent, and have a bit of time with her partner. As long as she keeps checking up that they are ok, and you do too, they should be fine.
Disappearing contributors - part 2
Have you stopped buying papers?
I am ashamed of her that she would do this. The boy's cry every time he brings them back to her. She feels they will be happier with him than hundreds of miles away from him with her.

nina