Forgot Grandkid's Name Again

Every time I'm at the playground with my grandkids, I just can't keep their names straight. It's like there are too many little ones running around and all they seem to have in common is this big bundle of energy. Today, as I was trying to hand a juice box to one of them, I called her by her sister's name instead. She looked at me with such confusion, like 'Grandma, really?' It's embarrassing because I know their parents would think it's sweet if they knew how hard I'm trying to remember. But honestly, is there anything worse than mixing up a kid's name in front of everyone? They're still so young, and already they seem to notice when you slip up.