Nami always loved kids. So it's only natural for her secret oni clone to become a babysitter. As for the crew? We've already got the original Nami. She's quite loved too, so another shouldn't be necessary.
She was, until Oda decided to have her join the straw hats group back on chapter 823 instead of stay on Zou. Now she's bonded with them, lived with them, saved them etc. Pedro saying that she will realise their significance one day. That's an actual bond.
That's funny because that's what I consider at "best" for Yamao. She's already doing such an amazing job looking after Momo. It would almost be cruel to take her away from her calling. Meanwhile Carrot has zero relations whatsoever with Momo since Oda built all of her relationships with Perospero (for the sake of the dawn + Pedro) and the straw hat crew.
Oda built new relationships between Carrot and the crew, whilst he instead built a new relationship between Yamao and Momo. I think we know who'll be stuck on diaper changing duty post Wano.