We went down to near Beziers last Easter break. We took a couple of days, as we are travelling from Central Scotland, so a longer drive this side too.... Our way of doing it was - leave here late afternoon to drive to Dover and get on the 1am ferry to Calais; Bit of a sleep on the ferry, and the passenger gets to sleep in the car as much as possible. We stopped the first night at Chartres, and then a second night near Volvic - largely in each case because we wanted to see a bit of the areas round about. Also, DD was 2.4, and we didn't really want her getting too grouchy in the car (hence the overnight on this side.) We use the peage as much as possible for the long stretches, and meant that you get cracking on a bit on the miles.
We've been down in that region a fair bit (before we had DD as well), and yes, I'd also agree with avoiding weekend travel in the summer if you can. It can be mental. Also, remember you will struggle in some places to find anywhere open on a Sunday for food/shopping. We found this out the hard way the first time!
The route via Millau is pretty impressive with the viaduct too - I'd definitely go that way in at least one direction. :) Loads of the service stations/peage stops have picnic areas too - we used them quite a bit. Watch out for 'Aire de....', and they usually have a bit for leg stretching - invaluable for a toddler, we found. Also, we tended to stay in Ibis hotels, purely because they had bigger rooms for families in most cases. The Campanile's are fine, but there is a certain amount of 'dancing' to be done around the child bed... I did find myself on it more than once, as once DD climbed into bed with us, there wasn't enough room, and DP was never going to fit into the 'free child bed for under 7s' - but, to be fair, I didn't exactly fit it either!
It's a beautiful part of the country - you'll have a great time, I'm sure. :)