The last nanny I hired did great with a set of twins and quickly made friends with the older child. The only issue I has with him was that some sort of glitch made him completely invisible and unselectable. So you could see and hear him talking, but not click on him. He'd go feed a baby and there'd be a floating baby with a bottle. It was particularly disturbing when he did the play interaction with them.
I finally fiddled around enough to solve his invisibility problem and he immediately seduced the husband of the family (damned autonomous woohoo) so that was the end of that.
As a nod to answering the initial question, butlers WILL care for children but WITH SOME NOTABLE EXCEPTIONS I've generally found nannies more reliable.