As an adult, you can’t force a child to connect with you. There are definitely things that will make a child more receptive to a non-parental adult in their life. They will probably feel more emotionally close with the grandparents they spend a lot of time with, versus the grandparents they maybe see once a year. At the end of the day, you really can’t force a relationship with anyone, whether they’re an adult or a child. The difference is that adults often don’t see children as full people who have autonomy in how they spend their time. Entitled adults believe that they should be able to hang out with a kid, doing whatever they want to do, and the kid should be happy about it. It doesn’t matter if you’re their aunt or their grandmother: a kid has a right to prefer to spend time with their favorite adults. 

This is especially relevant when talking about kids who have grown up with a difficult home life. If they haven’t been able to trust the adults who are supposed to take care of them, they might be wary of strangers, and there’s nothing wrong with that.