A lovely idea, but I fear doomed to failure because of the time limit you are imposing. You are suggesting that it

would be nice to stop off in Paris for a couple of hour to show our children some of the sites and lunch..(a very quick stop!!)

but I don't think you understand the scale of the problem, the size of Paris and the traffic and parking problems. The sites are really too far apart to do, apart from using a HoHo bus which will take up more than a couple of hours even on its own, and lunch will take more time, eating into your stopover time.

I think it's not the right time to do this ... devote a couple of days to this, with an overnight stop, either leaving your car outside the centre or using a hotel with a parking garage.

However you could make a stop .. overnight at least at Futuroscope, a science/cinema theme park just south of Poitiers on the A10. (http://en.futuroscope.com/)

Even though the Eurotunnel route means that you get to France much quicker than using the classic ferry, do remember that French time is an hour ahead of English time so it will be already later in the day when you hit French soil. Calais to Sarlat is certainly not a journey that I'd like to do in a day, beginning in the UK! Viamichelin suggests that the quickest route would take A MINIMUM OF 8.5 HOURS driving with no stops, and as you're on holiday, do try to make the drive part of the trip.

Try routing ideas on http://www.viamichelin.fr .. it may suggest other nice places to make a break, but do remember that you may also encounter heavy traffic in school holidays around the major towns and in the Dordogne where many folk have holiday homes.

Weve done this run agree with other use viamichelin to plan route this will also give you toll costs so you can have money ready when you get to the booth, or if you have one of martin lewis moneysaving expert recomend credit cards then use the carte blue lane , avoid paris if going by car in my humble opinion I think there are still bridge problems in rouen so be warned to watch for the diversion. We have stayed at the kyriad at mulsanne which is about as far as I would want to do in one day when leaving the uk. If your car is diesel fill up at carefour at eurocity remember most fuel stations closed on sunday. Re alcohol testers look up the latest info I think the law was recinded so now they are only a recomendation hi vis jacket needs to be inthe car with you not in the boot.

Futuroscope well worth the visit but you need a whole day. The campanille is in walking distance so no need to take the car..
Hope this helps

Gingernut

you are answering a post that is over a year old so I expect the original poster will have already taken the holiday.