Favoritism or just Kids?

I'm not sure what to make of this but it's driving my hubby mad and is annoyed.

When we are over at my in-laws with our 1 year old it's great but as soon as my MIL's other grandchild (2) comes by it's a lot about her. Well, the toddler demands a lot of attention from grandmother and my MIL gives no boundaries. I say it's a phase and the child has no other great connection to others (uncle, aunts) thanks to her parents - so she clings onto her grandmother. But my hubby gets pissed off because to him it's favoritism, he expressed that sometimes he's not comfortable leaving our toddler with grandmother when his niece is there because she's not capable to give her the attention she deserves.

Grandmother doesn't hold our baby anymore, take a walk, feed her snacks, play pretty much she sort of gets tossed to back to us or someone else.

Our child loves to be social and is incredibly outgoing. While the other is shy and quiet.

I'm trying to be rational and civil but I understand where he's coming from. How could I broach the subject with MIL about this?