The best opportunity for urban children to know what rural life is like is to live in the country during summer vacation.They are likely to broaden their perspective. or Living in the country during summer vacation is the best opportunity urban children have to know what urban life is like. "Living in the country during summer vacation" is what is called a noun clause. You should treat it like you would a noun, putting it before or after the verb to be.

Well, just little things, rural life generally doesn't have an article in front of it, arban is spelt urban, and pluralise perspective to perspectives. But the first sentance is a little bit clunky and difficult to get on the first go. I personally would say; Urban children living in the country during the summer vacation is the best opportunity to learn what rural life is like. But otherwise it is perfectly understandable ^_^