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.
I'm afraid I can't think what they are either, though they sound a bit like the Bunkle books, which I used to love, and which are available again on this website which has republished some old children's books - stuff from the 40s and 50s mainly.
Thank you both for answering - I am beginning to doubt my memory slightly and am wondering if it was just one or two books rather than a whole series. I may spontaneously remember the author one day and be able to find it!
Thank you for the other suggestions though - as they both the Children in the Barn and the Bunkle books look rather enjoyable and I may well try them out.