Harvest Moon: Tree of Tranquility, rival children?

I'm married to Chase, and all of the rival marriages have taken place. Candace and Julius, Calvin and Phoebe, Renee and Toby, and Anissa and Jin. They're all married. But what I can't figure out is how to meet all their children. Do I have to wait a certain amount of days after their marriage or something? Oh ya, and one more question, is there anything that has to do with the opening behind the waterfall in Caramel Falls? I can't enter it or anything, is there something that has to do with it? Please help me!