Sounds fantastic - we did a eurotrip a month or so ago and loved it; when we have children I think it's a fantastic way of seeing the continent. I can't speak of your travel itinerary as were more France/Belgium based but I also go with the rule that anything more than 4-5 hours in a car (with the exception of first and last day of holiday) would be difficult - for all concerned!
I would recommend making sure you have access, at some point, to a Wifi signal "just in case" - we took our mobiles with us but turned the data off (smartphone) so when on the third day it pissed it down and ruined our plans to go walk round Brugge properly, we had to seek out an alternative. I hate mobile phones at the best of times, but it really did come in handy to have a quick check of where was worth going nearby - I'd imagine especially so with children. I'd avoid using data at all abroad - your mobile network may try and convince you but they also sting you in charges unless you are contracted for it.
If you're driving toll roads it can get quite expensive, but the smaller roads can be pretty difficult to navigate, especially in bad weather!
Sounds really, really obvious but we bought 6 packs of bottled water (for about 1.50E) every day - although we'd driven long distances before on quite a lot of the roads you can be going for a long time without any form of services, in addition to the fact opening/closing hours differ.
Keep an eye out for where is cheapest fuel wise - Switzerland will sting you for fuel, so if you can get it before you cross over the border do it.