It depends a lot on the day you drive, if you go to Calais I assume you will be driving through Belgium and Luxembourg. Weekdays there are loads of trucks on the road, weekends in the summer very few (at least on the German motorways) I live in Germany and have had an overnight stop at Trier from where it took about four hours to drive to the channel. It can take five or even more on a busy weekend.
A tip about filling your car up, if possible stop for petrol in Luxembourg, if you are on the motorway there is a petrol station not long after you drive out of Belgium into Luxembourg, we find it has the cheapest petrol in all of the Benelux countries and Germany.

many thanks for that tip
we prob going on saturday. arriving in calais at 11ish (am)

We're in Scotland and have regularly used the Rosyth to Zeebrugge ferry (I assume Hull to Zeebrugge would be your option). Zeebrugge to Trier is about 6 hours. We did that journey with a 2 1/2 year old no problem. Our theory has always been to spend the time on the boat rather than in the car as the children have the freedom to move rather than being strapped in car seats. The year after we were near Trier, we took a 3 1/2 year old and an 8 month old to Lake Annecy in the Alps from Scotland via Zeebrugge and again it wasn't a problem.