I can also second the Novotel at Reims - we've stayed there to break up the journey on several occasions. Only thing I'd say is the first time we went the satnav gave us the wrong directions so we ended up going an extra junction on the motorway (I think they'd just opened a new section so following the road would have worked previously just not once the new bit was there) - so it's worth updating your satnav beforehand and watching carefully - it's really disheartening when you're tired to see your hotel a few metres away and then have to drive another 10 miles or so to get back to it!
It also has a reasonable sized supermarket and small shopping centre just over the road from it if you don't want to eat hotel food - several cheap and cheerful food options, including buying a picnic from the hypermarket.
We've also stayed in the Holiday Inn Express in Arras which is just by the train station - it had a really nice spacious airy family room that was L shaped so a bed in each bit meant it wasn't quite as everybody on top of each other as you can be in family rooms. I think they might have free breakfasts too (well, included in the price).
Depending on which direction you're going in, we've also stayed in a Novotel in Ypres (Iepers) in Belgium, which was just off the main square and a lovely town to have a stop off in. It's small enough to wander around but with lots of history and as there are lots of visitors, there are plenty of hotels, hostels and food places. The breakfast was expensive but there was a very nice bakery opposite so we just wandered over to get breakfast in the morning and then ate in our room or went out exploring and had it in a traditional cafe.
Whichever hotel you decide to go with, it's worth signing up online to their frequent traveller club/programme (they all have different names!). With the novotel one (which is valid for all the hotels in the chain including ibis, mercure, sofitel and more) they frequently have sales open to those in the club - I've managed to get half price bookings pretty much every time we've gone. The Holiday Inn Express also has better rates and often has deals on. The other thing is to also look on the big sites like expedia, booking.com and hotels.com as they sometimes have special deals with hotel chains. And finally check on the cash back sites - I've had 12% back on some hotel bookings, through expedia and through the novotel site (which I could combine with their club deal) to get really good deals.
If I'm travelling and need a stop over abroad I tend to look for Holiday Inn Express hotels first (nice breakfast buffet included in the price, makes life easy and even if you only have to pay for adults, other places often add another £10ish for each adult for breakfast which ups the overall cost quite a bit. Novotel comes next, then scouring expedia etc to see what else is good and around, before checking on the individual sites to see if there are better deals to be had on them...