Going for this long with a young family, I guess you will be well loaded up weight wise....
Last year in France we encountered a Police weight check in the area immediately after leaving an autoroute toll.
This showed us to be a significant 200 kilos over the MTPLM shown on the plate. Having weighed everything and added the values to the MIRO I was shocked.
On return to UK I had the van checked on the local weighbridge which as near as confirmed the police figure. Got the van emptied and rechecked to find wight nowhere near MIRO.
Subsequent correspondence with Bessacarr (Swift) resulted in an admission that van was wrongly plated, and new plate issued with +200Kg!
So moral is: get van weighed in holiday trim to be sure all is what you expect.
PS French police were very helpful-their checks were advisory-no fine. But they had trouble with old style UK driving licence, so I would make sure you have latest version. Finally, they also wanted to see proof of ownership of the van (I think France has a car-like registration document) I got by with my CRIS certificate, but you certainly need something.
Have a good time