Escape to Witch Mountain by Alexander Key

"Tony thrust his hands deep into his jeans and worriedly scuffed the gravel with the toe of one shoe. 'I don't get it, Tia. What's he doing here?'

Tia looked frightened. 'I don't know. I -- I'm afraid he's found out we're here, and has come to get us.'

'After all these years? That doesn't make sense. But what if he has come for us? I'd rather go with him any time then stay here -- I mean, if we had to stay here.'
'No!' She said fiercely. 'No! Never! It would be better to run away and go hungry. Much better. I -- I'd rather be dead than go with him.'" (32)

Tia and Tony are orphaned brother and sister who don't know where they come from. They were living with old "Granny" Malone, until she passed away and they were shipped to the Hackett House orphanage. While on a trip with the orphanage to a mountain-side camp, Tony and Tia have a chance meeting with a nun who might know their original family. While this gives them hope that they'll find their family and the source of their mysterious powers, a man claiming to be their uncle sends them fleeing for an unconfirmed safe haven in Witch Mountain, rumored to have witches living in its peaks. Alexander Key's Escape to Witch Mountain will have readers eager to find out what happens to Tony and Tia, and if they are witches.... or aliens.

AMY