Haki against Jewelry Bonney
There has been no proof of this yet, so I'm basing myself on Sugar's power and speculation. She has a similar power, where she can alter a person's body by touching them. We have seen Sugar turn a lot of Haki users into toys, so it is safe to say that Jewelry Bonny could also turn Haki users into babies.

But could they transform a Haki coated body? Well, Haki allows a user to touch the real person underneath, bypassing the Devil Fruit's power, so I would speculate that Haki would prevent someone from turning them into toys or babies, because the power would not be able to reach the victim.