We did Fife to Morzine this year with kids aged 9 and 11. We drove to Whitstable on the first day and stayed overnight with friends. Early eurotunnel (6:30am ish?) the next morning and drove 5 hours ish to Fontainebleau (from recommendations here). Spent 2 nights in Fontainebleau including a full day in Paris after getting the train in (40 mins and 5 euro pp). The drive to Morzine from there was about another 6 hours I think.
On the way back we left Morzine at about 7am and just blasted up to Calais in one hit with short lunch stop. Arrived at 5pm ish. Then tunnnel to Folkestone and another 2.5 hours to Peterborough to stay at my brother-in-laws. Next day we finished the journey home.
Overall it worked well. The worst bit was the first day driving down to Kent as we had some traffic issues and got diverted through country lanes etc off the A1.
In future I wouldn’t stop in Fontainebleau, I’d just do Calais to Morzine in one hit as we did on the return. We specifically did it this time as we wanted to take the kids to Paris. However it was a really nice place to visit so would recommend it as a stop option.
For us it makes sense really to drive through the UK as we have friends and family that live en route that it’s both convenient to stay with and good to see them, so killing two birds. Also, when you can use Tesco clubcard points to cover the Eurotunnel then the Hull ferry becomes even harder to justify. Just make sure the kids have got DVD players / iPads etc!