Pit stops when driving with kids
These days there are loads of fast food outlets such as MacDonalds along the major highways. Most have great playrooms.
I let the kids play whilst us adults eat our meals in peace, then just before we go they all have a toilet stop and then we order their food to take away.
That way they have used up some energy and stretched their legs, plus eating in the car also adds as a distraction for a period of time too.