I'm assuming there are no grandparents or aunts or anyone available to care for them, because I would NEVER leave my child alone for that long with someone I'd never met.
I would hire a nanny, if it were that long. Not just a baby sitter. Maybe an au-pair from overseas, who work for less and are funding their trip overseas.They're often happy to work for as little as $200 a week, less even. They're always hired through an agency.
But heavens! To leave children alone for that long with someone you and they don't know- if it were me, I'd bring the au-pair into my home for several weeks beforehand, to get to know them. I mean, these are the most precious lives of all here!