I dailed 911 and hung up HELP!?

well, to my own experience my little sister has done this on a working line, she dialed 911 and the police answered, she then hung up. almost immediatly they called us back asking us if we had an emergency and i said no but i explained to them it was my little sister and they just told me to not let my little sister grab the phone. it happened twice but the second time all that happened is the cops showed up at the house and asked to come in to be sure everything was okay since we dialed 911 accidently. long story short it shouldnt be a problem if they call you back or show up then explain other than that dont call them back