Quite old - they came in those little red hardbacks with a colourful picture on the dust cover. They are about a family called the Harveys (IIRC) four children early teen kind of age, - as in all these fifties type things, they are left to their own devices while for weeks on end while responsible adults swan off abroad on 'business', and the children have various adventures/crises to deal with.
Can't remember the author, and can't find anything to match on Amazon, - does anyone have a clue what I am on about. Think the author was a woman.