What are interesting happenings for my book?

I am writing a book called 'Smile Summer'. Its about an orphan who gets put in a foster home of a wealthy family with a famous dancer as a son. But he doesn't actually like his life and she conviences him to runaway with her. Soon enough the boy's parents have police chasing them and they end up falling in love. But...I need a big happening for my book. Like a problem , like all books have. Ideas please? :) thanks.