Is my niece on to something?

My niece is afraid to leave my sister. Now, my sister's kids have this spooky thing of being able to know things before they happen. My oldest nephew predicted when my gf was going to get pregnant.. and she did. Lately, my niece has been very clingy to my sister, not wanting to leave her. Many of you know that my sister is in a study for her melanoma. I really hope that nothing comes of this.. but I wanted to get my thoughts down.