Hello Bob,
I think I'll try and answer your questions in reverse order!
According to Autoroute (see map below) you should still take the Southern Dover to France crossing. You could take a crossing further North in the UK to Hook of Holland but it will be a very long sea crossing and won't save you much driving. It will also mean you'll be most likely driving on your own in Europe and there's safety in numbers. So my suggestion would be to drive to Dover or nearby on the 12th of May and stay one night in a Travelodge or similar. Then you can join our growing convoy of 131s for the 6:00am ferry from Dover to Dunkerque.
Regarding your 2 year old and wife, I'd say by all means bring them along but you know your lad best and you should know if he is going to be OK spending a very long time in a car or not. Once you are in Lossburg it won't be a problem as your wife and young lad can join in for the shorter drives and stay and enjoy the hotel and its facilities if they want on the other days. But getting there and getting back will be a couple of long all-day drives.
Driving on the wrong side of the road is not a problem. On the motorways you'll soon forget you are on the wrong side of the road. Once again this is where being in a convoy of 131s all driving on the wrong side of the road is better than being on your own.